Photonic switches, photonic switching fabrics and methods for data centers

ABSTRACT

Data center interconnections, which encompass WSCs as well as traditional data centers, have become both a bottleneck and a cost/power issue for cloud computing providers, cloud service providers and the users of the cloud generally. Fiber optic technologies already play critical roles in data center operations and will increasingly in the future. The goal is to move data as fast as possible with the lowest latency with the lowest cost and the smallest space consumption on the server blade and throughout the network. Accordingly, it would be beneficial for new fiber optic interconnection architectures to address the traditional hierarchal time-division multiplexed (TDM) routing and interconnection and provide reduced latency, increased flexibility, lower cost, lower power consumption, and provide interconnections exploiting scalable optical modular optically switched interconnection network as well as temporospatial switching fabrics allowing switching speeds below the slowest switching element within the switching fabric.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application claims the benefit of priority as a divisionalpatent application claiming priority from U.S. patent application Ser.No. 15/561,191 filed Sep. 25, 2017 entitled “Photonic Switches, PhotonicSwitching Fabrics and Methods for Data Centers”, which itself claimspriority as a 371 National Phase Patent Application of PCT/CA2016/000084filed Mar. 23, 2016 entitled “Photonic Switches, Photonic SwitchingFabrics and Methods for Data Centers”, which itself claims priority fromU.S. Provisional Patent Application No. 62/136,673 filed Mar. 23, 2015entitled “Photonic Switches, Photonic Switching Fabrics and Methods forData Centers”, the entire contents of each being included herein byreference.

FIELD OF THE INVENTION

This invention relates to photonic switches and photonic switch fabricsand more particularly to MOEMS photonic switching fabrics and photonicswitching fabrics with fast and slow spatial and wavelengthreconfiguration rates in combination for data center and cloud computingapplications.

BACKGROUND OF THE INVENTION

Cloud computing is, strictly, a phrase used to describe a variety ofcomputing concepts that involve a large number of computers connectedthrough a real-time communication network such as the Internet. However,today “the cloud” or “in the cloud” generally refers to software,platforms and infrastructure that are sold “as a service”, i.e. remotelythrough the Internet. Typically, the seller has actual energy-consumingservers which host products and services from a remote location, soend-users don't have to; they can simply log on to the network withoutinstalling anything. The major models of cloud computing service areknown as software as a service (SaaS), platform as a service, andinfrastructure as a service and may be offered in a public, private orhybrid network. Today, Google, Amazon, Oracle Cloud, Salesforce, Zohoand Microsoft Azure are some of the better known cloud vendorssupporting everything from applications to data centers a common themeis the pay-for-use basis.

Major cloud vendors provide their services through their own datacenters whilst other third party providers access either these datacenters or others distributed worldwide to store and distribute the dataon the Internet as well as process this data. Considering just Internetdata then with an estimated 100 billion plus web pages on over 100million websites, data centers contain a lot of data. With almost twobillion users accessing all these websites, including a growing amountof high bandwidth video, it's easy to understand but hard to comprehendhow much data is being uploaded and downloaded every second on theInternet. By 2016 this user traffic is expected to exceed 100 exabytesper month, over 100,000,000 terabytes per month, or over 42,000gigabytes per second. However, peak demand will be considerably higherwith projections of over 600 million users streaming Internethigh-definition video simultaneously at peak times.

All of this data will flow to and from users via data centers andaccordingly between data centers and within data centers so that theseIP traffic flows must be multiplied many times to establish total IPtraffic flows. Data centers are filled with tall racks of electronicssurrounded by cable racks where data is typically stored on big, fasthard drives. Servers are computers that take requests to retrieve,process, or send data and access it using fast switches to access theright hard drives. Routers connect the servers to the Internet. At thesame time these data centers individually and together providehomogenous interconnected computing infrastructures. At the same time asrequiring a cost-effective yet scalable way of interconnecting datacenters internally and to each other many datacenter applications areprovided free of charge such that the operators of this infrastructureare faced not only with the challenge of meeting exponentiallyincreasing demands for bandwidth without dramatically increasing thecost and power of their infrastructure. At the same time consumers'expectations of download/upload speeds and latency in accessing contentprovide additional pressure.

Fiber optic technologies already play critical roles in data centeroperations and will increasingly. The goal is to move data as fast aspossible with the lowest latency with the lowest cost and the smallestspace consumption on the server blade and throughout the network.According to Facebook™, see for example Farrington et al in “Facebook'sData Center Network Architecture” (IEEE Optical InterconnectsConference, 2013 available athttp://nathanfarrington.com/presentations/facebook-optics-oida13-slides.pptx),there can be as high as a 1000:1 ratio between intra-data center trafficto external traffic over the Internet based on a single simple request.Within data center's 90% of the traffic inside data centers isintra-cluster.

Accordingly, it would be beneficial to enhance connectivity within datacenters at multiple levels such as chip-to-chip, server-to-server,rack-to-rack, and cluster-to-cluster exploiting photonic interconnectionarchitectures to address the multiple conflicting demands. It would befurther beneficial to exploit photonic integrated circuit devices thatsupport large photonic switch fabrics employing space and/or wavelengthdomains but have slower switching speeds by providing distributedphotonic switch fabrics employing combinations of fast and slow photonicswitching elements allowing these to provide reduced latency, increasedflexibility, lower cost, lower power consumption, and provide highinterconnection counts.

It would be further beneficial to be able to leverage the transparencyand low latency within optical switching to enhance connectivity andreduce latency across the Internet and within web scale datacenters byexploiting optical switching. However, to date switching technologiesexploiting three dimensional (3D) microelectromechanical systems (MEMS)or two dimensional (2D) Mach-Zehnder Interferometer (MZI) based opticalswitches have not justified the business case for optical switchingwithin the datacenter. However, 2D planar microoptoelectromechanicalsystems (MOEMS) based optical switching provides the required features,performance, scalability, and cost balance to meet the datacenterbusiness case and accordingly the establishment of optical switch blocksand matrices will support network deployments for the Internet.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

SUMMARY OF THE INVENTION

It is an object of the present invention to mitigate limitations in theprior art relating to optical networks and more particularly towavelength division multiplexed networks for data center and cloudcomputing applications.

In accordance with an embodiment of the invention there is provided asystem for interconnecting a first set of leaf switches associated witha first spine switch and a second set of leaf switches associated with asecond spine switch without routing through at least one of the firstand second spine switches by providing a modular optically switched(MOS) interconnection network allowing programmable allocation ofbandwidth from ports on each of the first set of leaf switches to portson each of the second set of leaf switches.

In accordance with an embodiment of the invention there is provided amethod of establishing a switching fabric providing a reconfigurationrate at a higher speed than that defined by the slowest switchingelement within the switching fabric comprising providing an inputtemporal switch array, a plurality of spatial switching fabrics, and anoutput temporal switch array wherein a configurable spatial switchingfabric of the plurality of spatial switching fabrics other than thecurrent active spatial switching fabric of the plurality of spatialswitching fabrics is configured to a new configuration before the inputand output temporal switch arrays route all optical signals to theconfigurable spatial switching fabric of the plurality of spatialswitching fabrics.

In accordance with an embodiment of the invention there is provided amethod of establishing a switching fabric providing a reconfigurationrate at a higher speed than that defined by the slowest switchingelement within the switching fabric comprising providing an inputtemporal switch array, a plurality of spatial switching fabrics, and anoutput temporal switch array wherein a path between a predeterminedoutput port of the input temporal switch array and a predetermined inputport on the output temporal switch array on a predetermined spatialswitching fabric of the plurality of spatial switching fabrics otherthan the current active spatial switching fabric of the plurality ofspatial switching fabrics coupled to the predetermined output port ofthe input temporal switch array is configured to the new configurationbefore the input and output temporal switch arrays route all opticalsignals to the configurable spatial switching fabric of the plurality ofspatial switching fabrics.

In accordance with an embodiment of the invention there is provided amethod of establishing a configuration of a second remote switch from aplurality of first switches by coupling into a predetermined subset ofthe outputs of each first switch out of band signaling signals anddetermining the configuration of the second remote switch from the outof band signaling signals from the plurality of first switches.

In accordance with an embodiment of the invention there is provided amethod of switching wherein a first optical waveguide upon a beamextending from a pivot is rotated relative to the pivot point under theaction of a first MEMS actuator laterally disposed relative to the beamso that the first optical waveguide evanescently couples to a secondoptical waveguide of a plurality of second optical waveguidesgeometrically disposed based upon at least the beam, pivot point, andthe first MEMS actuator.

In accordance with an embodiment of the invention there is provided anoptical switch comprising:

a first waveguide portion having first and second input waveguidesformed thereon;

a second waveguide portion having first and second output waveguidesformed thereon;

a suspended waveguide portion having a plurality of optical waveguidesformed thereon; and

a MEMS actuator coupled to the suspended waveguide portion; wherein

-   -   in a first position the MEMS actuator positions the suspended        waveguide portion such that a first subset of the plurality of        optical waveguides are evanescently coupled to the first and        second waveguide portions placing the switch into a first state;        and    -   in a second position the MEMS actuator positions the suspended        waveguide portion such that a second subset of the plurality of        optical waveguides are evanescently coupled to the first and        second waveguide portions placing the switch into a second        state.

In accordance with an embodiment of the invention there is provided anoptical switch comprising:

a non-suspended waveguide portion having first and second waveguidesformed thereon; and

first and second suspended waveguide portions each having an opticalwaveguide formed thereon;

first and second MEMS actuators coupled to the first and secondsuspended waveguide portions;

-   -   wherein    -   in a first position the first and second MEMS actuators position        the suspended waveguide portions such that they are optically        coupled to the first and second waveguides within the        non-suspended waveguide portion placing the switch into a first        state; and    -   in a second position the first and second MEMS actuators        position the suspended waveguide portions such that they are not        optically coupled to the first and second waveguides within the        non-suspended waveguide portion placing the switch into a second        state.

In accordance with an embodiment of the invention there is provided anoptical switch comprising:

a non-suspended waveguide portion having first and second waveguidesformed thereon; and

first and second suspended waveguide portions each having an opticalwaveguide formed thereon; wherein

-   -   in a first configuration the suspended waveguide portions are        positioned such that they are coupled to the first and second        waveguides within the non-suspended waveguide portion placing        the switch into a first state; and    -   in a second configuration the suspended waveguide portions are        positioned such that they are not coupled to the first and        second waveguides within the non-suspended waveguide portion        placing the switch into a second state.

In accordance with an embodiment of the invention there is provided anetwork comprising interconnecting a plurality of electronic packetswitches within a first tier via a plurality of optical switches withina second tier in order to form a two-tier folded Clos network topology,wherein the plurality of optical switches are not directly opticallyinterconnected to each other, and each electronic packet switch isconnected to multiple optical switches.

In accordance with an embodiment of the invention there is providedswitching element comprising electronic packet switching and opticalswitching, the switching element for switching between a plurality ofservers coupled to the switching element within a rack as a “top ofrack” switch and at least another electronic device remotely located.

In accordance with an embodiment of the invention there is provided asystem comprising:

-   a plurality R optical cables each coupled to a plurality of P    parallel lane pluggable optical transceivers; and-   an optical switch matrix comprising a plurality P of M×N optical    switch planes, wherein each optical cable is connected to the    plurality P of M×N optical switch planes at least one of:    -   statically by association of a predetermined parallel lane of        the P parallel lane pluggable optical transceiver to an M×N        optical switch plane of the plurality P of M×N optical switch        planes; and    -   dynamically by optical switching matrices forming part of the        optical switch matrix such that one or more multiple pull-out        connectors assembled onto the optical cable are coupled to        multiple pull-out connectors onto the optical switch matrix.

In accordance with an embodiment of the invention there is provided amethod of optical switching comprising establishing an optical couplingbetween a first optical waveguide of a plurality of first opticalwaveguides upon a movable element of a MOEMS based optical switch and atleast one second optical waveguide of a plurality of second opticalwaveguides upon a fixed element of the MOEMS based optical switch,wherein

-   -   in a first state the MOEMS based optical switch has optical        coupling between the first optical waveguide and the second        optical waveguide, and    -   in a second state the MOEMS based optical switch has no optical        coupling between the first optical waveguide and the second        optical waveguide.

In accordance with an embodiment of the invention there is provided amethod of optical comprising wherein a first optical waveguide upon abeam extending from a pivot is rotated relative to a pivot point of thepivot under the action of a first MEMS actuator laterally disposedrelative to the beam so that the first optical waveguide butt couplesacross an air gap to a second optical waveguide of a plurality of secondoptical waveguides geometrically disposed based upon at least the beam,pivot point, and the first MEMS actuator.

In accordance with an embodiment of the invention there is providedoptical switch comprising:

-   a movable MEMS element of the optical switch supporting a first    optical waveguide and a second optical waveguide wherein the first    optical waveguide and a second optical waveguide intersect at an    angle high enough to limit optical coupling between the first    optical waveguide and a second optical waveguide;-   a curved optical waveguide disposed upon the movable MEMS element    having a first end disposed towards a first end of the first optical    waveguide and a second end disposed towards a first end of the    second optical waveguide;-   third and fourth optical waveguides supported upon a fixed portion    of the optical switch; wherein-   the movable MEMS element in a first state couples each of the third    and fourth optical waveguides to the first end of a respective one    of the first optical waveguide and the second optical waveguide; and-   the movable MEMS element in a second state each of the third and    fourth optical waveguides are coupled to an end of the curved    optical waveguide.

In accordance with an embodiment of the invention there is provided anoptical switch matrix comprising:

-   a plurality of inputs at a first end of the optical switch matrix;-   a plurality of outputs at a second distal end of the optical switch    matrix;-   a plurality of unit cells, each unit cell comprising:-   a movable MEMS element of the optical switch supporting a first    optical waveguide and a second optical waveguide wherein the first    optical waveguide and a second optical waveguide intersect at an    angle high enough to limit optical coupling between the first    optical waveguide and a second optical waveguide;-   a curved optical waveguide disposed upon the movable MEMS element    having a first end disposed towards a first end of the first optical    waveguide and a second end disposed towards a first end of the    second optical waveguide;-   third and fourth optical waveguides supported upon a fixed portion    of the optical switch; wherein-   the movable MEMS element in a first state couples each of the third    and fourth optical waveguides to the first end of a respective one    of the first optical waveguide and the second optical waveguide; and-   the movable MEMS element in a second state each of the third and    fourth optical waveguides are coupled to an end of the curved    optical waveguide;-   wherein adjacent unit cells disposed along the other edges between    the first end of the optical switch matrix and the second end of the    optical switch matrix are coupled sequentially to each other via a    reflective mirror.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described, by way ofexample only, with reference to the attached Figures, wherein:

FIG. 1 depicts a datacenter network according to the prior art;

FIG. 2 depicts a two-tier leaf spine architecture according to anembodiment of the invention supporting scaling out;

FIGS. 3 and 4 depict a Modular Optically Switched (MOS) networkarchitecture for web scale data centers applied at the leaf switch andspine switch levels respectively;

FIGS. 5A and 5B depict rack mounted embodiments of a Modular OpticalSwitch (MOS) together with exemplary modular fiber shuffleinterconnection element according to an embodiment of the invention;

FIGS. 6A and 6B depict an interconnection between two MOS according toan embodiment of the invention;

FIG. 7 depicts a Scaled Out Optical Switched (SOOS) network architecturefor web scale data centers according to an embodiment of the invention;

FIG. 8 depicts Ethernet switch port counts for SOOS architectureaccording to FIG. 7 against a prior art 3-Tier Clos Non-BlockingLeaf-Fabric-Spine switch versus number of computer servers;

FIGS. 9 to 11 depict an optical switching technology exploitingMOEMS-turning silicon (MOTUS) supporting photonic switching fabrics suchas MOS and SOOS as depicted in FIGS. 3 to 8;

FIG. 12 depicts a 4×4 photonic switch fabric exploiting multipleinstances of MOTUS on the same die providing reduced crossover count,perpendicular crossovers, and a strictly non-blocking architectureaccording to embodiments of the invention;

FIG. 13 depicts 4×4 and 8×8 optical switch matrices according toembodiments of the invention employing MOTUS optical engines anddirectional couplers for enhanced layout and reduced cross-overs;

FIG. 14 depicts an architecture for spatial diversity photonic switchingfabric employing an initial time domain switching planes according to anembodiment of the invention;

FIG. 15 depicts the architecture of FIG. 14 applied to an exemplary 4×4strictly non-blocking spatial diversity fabric and as a generalizedarchitecture of n channels in conjunction with m-order time domaindiversity of N×N core spatial diversity fabric;

FIG. 16 depicts the architecture of FIG. 14 applied to an exemplary 8×8spatial diversity fabric with 2-time domain diversity channels inconjunction with 8×8 core spatial diversity re-arrangeable non-blockingfabrics;

FIG. 17 depicts the architecture of FIG. 14 applied to an exemplary 8×8spatial diversity fabric with 2 and 4-time domain diversity channels inconjunction with 8×8 and 4×4 core spatial diversity re-arrangeablenon-blocking fabrics;

FIG. 18 depicts the architecture of FIG. 14 applied to an exemplary16×16 spatial diversity fabric with 4-time domain diversity channels inconjunction with 16×16 core spatial diversity re-arrangeablenon-blocking fabrics with concurrent spatial diversity fabricutilization;

FIG. 19 depicts an out of band synchronization mechanism between a pairof optical circuit switches according to an embodiment of the invention;

FIGS. 20A to 20C depict a direct waveguide-waveguide MOEMS opticalswitches without mirror elements employing pivoting suspended waveguideand dual lateral latching actuators for asymmetrically latching todouble latching positions;

FIG. 21A depicts a 4×4 an expandable crossbar switch matrix composed of16 2×2 switching elements;

FIG. 21B depicts 4×4, 8×8, and 64×64 crossbar matrices exploiting 2×2switching elements;

FIGS. 22A and 22B depict 2×2 switching elements according to embodimentsof the invention exploiting MOEMS elements, whereas the MEMS containsbar waveguide and cross waveguide and couples evanescently toinput/output waveguide;

FIG. 23A depicts the 2×2 switching element according to the embodimentof the invention depicted in FIGS. 22A and 22B in a “default” state;

FIG. 23B depicts the 2×2 switching element according to the embodimentof the invention depicted in FIGS. 22A and 22B in “bar” and “cross”states;

FIG. 24 depicts a 2×2 switching element according to an embodiment ofthe invention exploiting 2 MOEMS elements and optical evanescentcoupling using a single crossing;

FIGS. 25A and 25B depict a latching 2×2 switching element according toan embodiment of the invention exploiting MOEMS elements and opticalevanescent coupling in “cross” and “bar” states respectively;

FIGS. 25C and 25D depict a latching 2×2 switching element according toan embodiment of the invention exploiting MOEMS elements and opticalevanescent coupling in “cross” and “bar” states respectively;

FIGS. 26A and 26B depict a latching 2×2 switching element according toan embodiment of the invention exploiting MOEMS elements and opticalevanescent coupling in “cross” and “bar” states respectively requiringMEMS actuators only for the latching;

FIGS. 27A and 27B depict cross-sectional views of the latching 2×2switching element according to FIGS. 26A and 26B without limiterstructures and employing waveguide dielectric cladding as limiter forthe gap closing mechanism formed using RIE etching processes accordingto an embodiment of the invention

FIG. 28A depicts cross-sectional views of linear motion MOEMS basedvertical optical coupling elements according to embodiments of theinvention;

FIG. 28B depicts cross-sectional views of a rotary motion MOEMS basedvertical optical coupling element according to an embodiment of theinvention;

FIG. 29A depicts an 1×2 optical switching element and 4×4/3×4 opticalswitch matrices employing such an 1×2 optical switching element;

FIG. 29B depicts a linear motion MOEMS based 1×2 optical switchingelement exploiting the topology depicted in FIG. 29A for the 1×2switching element according to an embodiment of the invention;

FIG. 30 depicts the linear motion MOEMS based 1×2 optical switchingelement depicted in FIG. 29B according to an embodiment of the inventionin bar and cross-states wherein the waveguides are shown with a gap forclarity;

FIG. 31 depicts 2×2 and 3×3 optical switching circuits according to anembodiment of the invention exploiting linear motion MOEMS based 1×2optical switching element according to FIGS. 29B and 30;

FIG. 32 depicts an 8×8 optical switching matrix exploiting linear motionMOEMS based 1×2 optical switching element depicted in FIG. 29B accordingto an embodiment of the invention to provide Path Independent Loss(PILOSS) switching;

FIG. 33 depicts a rotary motion MOEMS based 2×2 blocking opticalswitching element according to an embodiment of the invention;

FIGS. 34 and 35 depict a rotary motion MOEMS based 1×5 optical switchingelement according to an embodiment of the invention;

FIG. 36 depicts electro-static gap closing within a rotary motion MOEMSbased 1×5 optical switching element according to an embodiment of theinvention; and

FIG. 37 depicts self-alignment in conjunction with electro-static gapclosing within a rotary motion MOEMS based 1×5 optical switching elementaccording to an embodiment of the invention.

DETAILED DESCRIPTION

The present invention is directed to optical networks and moreparticularly to use optical switching in data center and cloud computingnetworks.

The ensuing description provides exemplary embodiment(s) only, and isnot intended to limit the scope, applicability or configuration of thedisclosure. Rather, the ensuing description of the exemplaryembodiment(s) will provide those skilled in the art with an enablingdescription for implementing an exemplary embodiment. It beingunderstood that various changes may be made in the function andarrangement of elements without departing from the spirit and scope asset forth in the appended claims.

1. Current State of the Art without Optical Switching in Intra-DataCenter Communications

The majority of warehouse scale datacenters networks today are designedaround a two-tier leaf/spine Ethernet aggregation topology leveragingvery high-density switches. Servers first connect to leaf switches andthen leaf switches connect to spine switches. Each leaf switch mustconnect to every spine switch in order to ensure that the network isnever oversubscribed at any location beyond the chosen oversubscriptionthreshold. By using such a network topology, and leveraging an equalcost multi-path protocol (ECMP), it is then possible to have an equalamount of bandwidth across the aggregated path between the upstream anddownstream thereby providing a non-blocking network architecture viamultiple aggregated link. The number of uplinks on the leaf switcheslimits the number of spine switches to which they can connect. Thenumber of downlinks on the spine switches then limits the number of leafswitches that can be part of the overall network.

Consequently, the number of computer servers that can be added totwo-tier leaf/spine datacenter network architecture is a direct functionof the number of uplinks on the leaf switches. A fully non-blockingtopology requires that leaf switches have as much uplinks bandwidth asdownlink bandwidth to computer servers. In contrast in FIG. 2, in atwo-tier leaf/spine architecture according to an embodiment of theinvention then it only scale out to add a maximum amount of serverswithin the chosen oversubscription parameter and at a constant latency,because every leaf switch is connected to every spine switch.Accordingly, to achieve this and scale out, the bandwidth of leaf switchuplinks at 40 Gbps is instead broken out as 4 links of 10 Gbps that arethen connected to 4 distinct spine switches. Hence, more uplinks connectto more spines and thence more leaf switches and servers can besupported.

2. Leaf-Spine Connectivity Developments

Two-tier Leaf-Spine architectures have become the standard in datacenter network architectures and are known to the skilled in the art.The first tier is made of switches defined as leaves. The second tier ismade of switches defined as Spines. In a three-tier network topology,there could be a second tier of leaf switches intermediating the firsttier of leaf switches and a third tier made out of spine switches. Forthe purpose of the present patent application, a second tier of leafswitches would be referred as spine switches.

2A: Modular Optically Switched (MOS) Connectivity ExploitingReconfigurable Optical Tunable Transmitters and Receivers

Whilst WDM based ring networks can provide reduced latency between leafnodes as well as a degree of programmable capacity between leaf nodes byremoving the requirement for interconnection between spline switches aswell as a programmable CDC optical switch to provide cross-ringconnectivity. Such WDM ring based networks provide “within” splinelatency reduction. However, the historical design methodologies basedupon cost effective Ethernet switches, equal cost Multi-Path loadbalancing and simple hashing algorithms unaware of flow dimensions areinefficient when low capacity flows encounter congestion due to apreponderance of high capacity flows. Today with approximately 80% ofthe east-west traffic within a network representing less than 10% of thenumber of flows such scenarios are increasingly common. Within the priorart centralized traffic engineering may help improve overall networkutilization at the expense of local knowledge routing. Accordingly,prior art architectures do not address short-lived latency sensitive lowcapacity flows that are choked by long-lived bandwidth-hungry highcapacity flows thereby degrading application performance.

However, traffic engineering is challenging given that the goal is tosave these low capacity flows whilst preventing high capacity flows fromconflicting in order to avoid impacting these low capacity flows, orworst, the high capacity flows stall completely. With growingpopulations of both flows that is temporarily, or permanently, greaterthan any given Ethernet switch may be able to track, a way to scale outan architecture may be to drastically increase the number of addressableoptical paths in the network and divert the “elephant” flows ontodedicated point to point optical paths. Solutions to offload data centerleaf-spines from “elephant” flows, based on three dimensional (3D) MEMSM×N optical switches are now entering the market but as these solutionsare based on optical switches designed for patch panel automation theyare not modular, do not exhibit scale out properties, have a highacquisition cost and require centralized traffic engineering. Further,as 3D MEMS are based on free space optics, they are complex to packageand bulky.

Accordingly, the inventors have established a Modular Optically Switched(MOS) network architecture, such as depicted in FIG. 3, exploitingseveral instances of a single construct element, namely a 1×N, e.g.N=32, planar optical switch based upon novel microoptoelectromechanicalstructures (MOEMS) comprising MEMS rotational mirrors integrated withoptical waveguides. Exploiting large-scale silicon photonics integrationmakes it possible to integrate multiple planar MOEMS optical switchinstances onto a single silicon chip. It then becomes possible tomanufacture hundreds of optical switches per silicon wafer and obtain acost structure similar to what is possible within the microelectronicsindustry. For example, a system level product, a 64×2048 modular opticalswitch, may be integrated onto a single printed circuit board byemploying 64 instances of these 1×32 planar optical switches. Due totheir compact 2D MOEMS such a modular optical switch can then fit into adata center single rack unit configuration and make a stack of modularoptical switches attractive to deploy and easy to interconnect togetherin the same cabinet.

A scale out modular optical switch (MOS) according to embodiments of theinvention may be deployed in tandem with every top of rack (ToR) switchwith or without a leaf switch level WDM ring network such as describedin respect of FIGS. 4 and 5 and the corresponding patent application ofthe inventors, U.S. Provisional Patent Application 61/950,238 entitled“Methods and Systems Relating to Optical Networks” filed Mar. 10, 2014and associated World Intellectual Property Office Patent CooperationTreaty Application entitled “Methods and Systems Relating to OpticalNetworks” filed Mar. 10, 2015. A MOS allows users to maintain the scaleout and economic properties of web scale data center networks toincreased data center dimensions. Accordingly, the ToR switches can makeuse of distributed local knowledge routing to assign “elephant” flowsonto point-to-point optical paths to other ToRs without implementingnetwork wide traffic engineering.

Top of Rack (ToRs) are switches installed in a data center cabinet(rack) above all the servers within that rack. They sit at the very edgeof the data center network and connect the servers to each other and tothe network infrastructure. Based on exemplary leading Ethernet switchesthen prevalent configurations for ToRs for the foreseeable future willexploit 32 ports of Quad Small Form-factor Pluggable interfacessupporting QSFP+10 Gbps 4× transceivers (QSFP10 or QSFT+) and evolvingto QSFP 28 Gbps 4× transceivers (QSFP28) in a single rack unitconfiguration. Their low cost enables their use as spine switches inscale out designs. The QSFP+(QSFP10) interface enables 4 pairs of duplexlanes of 10 Gbps per ToR port, for a total of either 32 ports of 40 Gbpsor 128 ports of 10 Gbps, using parallel lanes QSFP+pluggable optics &break-out cables. The QSFP28 interface enables 4 pairs of duplex lanesof 25 Gbps per ToR port, for a total of 32 ports of 100 Gbps, 64 portsof 50 Gbps, or 128 ports of 25 Gbps, using parallel lanes pluggableoptics & break-out cables.

The Modular Optically Switched (MOS) reference network architecture(RNA) depicted in FIG. 3 leverages the fact that ToRs can use parallellane pluggable optics. These ToRs now not only have enough interfaces toconnect a full rack of servers, but also enough interfaces to providefor the necessary connectivity to both the Ethernet spine switches ofthe data center leaf-spine and the modular optical switches of the MOSRNA. Within MOS RNA presented in FIG. 3 each Spine Switch 150 supportsconnections to 16 ToR Leaf Switches 140 and between a pair of SpineSwitches 150 and their associated 32 ToR Leaf Switches 140 there isdisposed a MOS 650 comprising 32 interconnected modules MOS #1 to MOS#32, labelled 610(1) through 610(32). Within an exemplary MOS RNA theinventors propose that the ports of a 32-port QSFP+ ToR are allocated asfollows:

-   -   sixteen QSFP+ ports to 16 Servers 130 in the rack at 40 Gbps        each or though parallel lane pluggable optics and breakout        cables as 64 ports of 10 Gbps to 64 server ports in the rack        (supporting up to 64 Server 130 according to design);    -   eight QSFP+ ports of 40 Gbps to 8 Ethernet Spine Switches 150 or        through parallel lane pluggable optics and breakout cables as 32        ports of 10 Gbps to up to 32 Spine Switches 150 (or other        combinations such as 40 Gbps to adjacent Spine Switches 150, 20        Gbps to next pair of nearest neighbour Spine Switches 130 and 10        Gbps to next 8 Spline Switches 150 either way); and    -   eight QSFP+ ports of 40 Gbps connected to MOS 650 with parallel        lane pluggable optics and breakout cables.

Within the MOS RNA 650 the focus is not towards the ports on the ToRLeaf Switches 140 which are connected to the Ethernet spine switches asthis portion of the network behaves like any existing 2:1 oversubscribedleaf-spine. The novelty in the MOS network architecture lies in theports on the ToR Leaf Switches 140, which are connected to the modularoptical switches within the 32 interconnected modules MOS #1 610(1) toMOS #32 610(32). Once the eight QSFP+ ports of a ToR Leaf Switch 140 areconnected to a single MOS module 610(X) modular optical switch then eachof the individual 32 pairs of lanes of the parallel lane pluggableoptics (40 GBase PSM4) are connected to individual 1:32 planar opticalswitches supporting therefore up to 1024 degrees of interconnectionthrough the MOS modules MOS #1 610(1) to MOS #32 610(32) for each ToRLeaf Switch 140 connected to the MOS 650 network.

In the MOS RNA 650 each of the 32 ToR Leaf Switches 140 are connected toa separate MOS module 610(X). Then, by interconnecting the MOS modules610 together across their fiber shuffles, it become possible to scaleout the MOS RNA 650 to the following capacity given a full scale row/podconfiguration of 32 racks/32 ToR Leaf Switches 140 with up to 2,048server interfaces at 10 Gbps. In addition to a total capacity of 10.24Tbps across the Ethernet switched leaf-spine network the followingadditional bandwidth across the scaled out MOS RNA 650 is available:

-   -   Point-to-point bandwidth between any two given ToR Leaf Switches        140 across the eight QSFP+ interfaces directly of 320 Gbps;    -   Bisection bandwidth in a row of 32 ToR Leaf Switches 140 each        with eight QSFP+ interfaces: 2.64 Tbps;    -   Addressable bandwidth in a row of 32 ToRs, each with eight QSFP+        interfaces: 327.68 Tbps.

As the optical switches within the MOS 650 are protocol independent thenby replacing the ToR Leaf Switches 140 32-port QSFP10 interfaces to32-port QSFP28 interfaces and upgrading the Spine Switches 150 thosewith QSFP28 interfaces it then becomes possible to attain a full-scaleconfiguration of 32 racks capable of interconnecting 2,048 serverinterfaces at 25 Gbps each. In addition to a total capacity of 25.6 Tbpsacross the Ethernet switched leaf-spine, the following additionalbandwidth across the Modular Optically Switched network is achieved:

-   -   Point-to-point bandwidth between any two given ToR Leaf Switches        140 across eight QSFP+ interfaces: 800 Gbps;    -   Bisection bandwidth in a row of 32 ToR Leaf Switches 140, each        with eight QSFP+ interfaces: 6.6 Tbps; and    -   Addressable bandwidth in a row of 32 ToR Leaf Switches 140, each        with eight QSFP+ interfaces: 819.2 Tbps.

Such large east-west bandwidth capacity is achievable through theinterconnection of 32 individual MOS modules 610, which can be installedcoincidentally with the ToRs, in a true scale out and highly resilientfashion. In the MOS RNA 650, this is all made possible by theinterconnection of 2,048 individual 1:32 planar optical switchinstances, distributed equally amongst the 32 modular optical switches.It would be apparent that the MOS RNA 650 directly interconnecting ToRLeaf Switches 140 within a single leaf-spine and/or between multipleleaf-spine arrays reduces the latency between the connected ToR LeafSwitches 140

It would be evident that the MOS RNA 650 depicted in FIG. 3 may bevaried without departing from the scope of the invention. For example,the 1:32 planar optical switches may be replaced with 1:48, 1:16, or1:64 planar optical switches or other port counts to interconnect adifferent number of ToR Leaf Switches 140 and/or ToR Leaf Switches 140within each leaf-spine array. Optionally, the MOS RNA 650 may supportoperation in conjunction with or in isolation from a WDM ring networkinterconnecting the ToR Leaf Switches 140. Similarly, the MOS RMA maysupport operation in conjunction with or in isolation from a WDM ringnetwork interconnecting the Spine Switches 150. Optionally, the MOS RNA650 may be implemented at a higher level, such as depicted in FIG. 4wherein a MOS RNA 650 is connected to the Spine Switches 150 in additionto the MOS RNA 650 coupled to the Leaf Switches 140.

Referring to FIGS. 5A and 5B there are depicted 4U Rack Unit 710 and 1URack Unit 720 implementations of a MOS RNA 650 are depicted. Referringto 4U Rack Unit 710 then considering the MOS RNA 650 in FIG. 3 there are8 connectors on the upper left labelled Q1 to Q8 which are eachconnected to a QSFP+(QSFP10) port of a ToR Leaf Switch 140 and hence the4U Rack Unit 710 receives on each connector 4×10 Gbps transmit channelsand provides 4×10 Gbps receive channels back to the ToR Leaf Switch 140.Within the 4U Rack Unit 710 these channels are coupled to one of fourmodules 730A to 730D such that these receive/provide the signals forQ1/Q2, Q3/Q4, Q5/Q6, and Q7/Q8 respectively. Accordingly, within eachmodule the received 8 transmit signals are coupled to 8 1:32 transmit(Tx) optical switches (OS) 740 whilst the 8 receiver channels arecoupled to 8 32:1 receive (Rx) optical switches 770. Each TxOS 740within a module may therefore route to one of 32 output ports 760 whichare labelled C1 to C32, which are themselves multiway connectors, andthe received signals from these 32 output ports 760 C1 to C32 arecoupled to the RxOS 770. As such the 4U Rack Unit 710 depicted receiveson the 8 connectors Q1 to Q8 8×(4×10 Gbps) and routes these 32 10 Gpbschannels as either 8×(4×10 Gbps) to 8 output connectors 760 from C1 toC32 or as 32×(1×10 Gbps) to all output connectors 760 C1 to C32 or16×(2×10 Gbps) to 16 output connectors 760 from C1 to C32 or othercombinations thereof.

As depicted each one of the four modules 730A to 730D, identified asModule W, Module X, Module Y, Module Z provide transmit signals forQ1/Q2, Q3/Q4, Q5/Q6, and Q7/Q8 respectively to the ranks W, X, Y, and Zof output connectors 760 C1 to C32 within the single 4U Rack Unit 710via the TxOS 740. At the same time the RxOS 770 within each module routereceived signals on the ranks W, X, Y, and Z of output connectors 760 C1to C32 to the Q1/Q2, Q3/Q4, Q5/Q6, and Q7/Q8 connectors. Alternatively,a single module, e.g. Module W 730A, may be housed within a single 1URack Unit 720. Optionally, all the functionality within the 4U Rack Unit710 may be housed within a 1U Rack Unit 720. Optionally, the connectorcount may be reduced for interconnecting between MOS units within either4U Rack Units 710 or 1U Rack Units 720 through the use of higher countconnectors, e.g. MPO24 24 fiber connectors rather than MPO12 12 fiberconnectors.

It would therefore be evident that 4U Rack Units 710 or 1U Rack Units720 may therefore be connected through their C1 to C32 connectors to oneanother and therein to their respective Leaf Switch or Leaf Switches. Anexemplary interconnection being depicted in FIGS. 6A and 6B withinterconnection mapping 700 part of which is expanded in expanded view750.

2B: Scaled Out Optically Switched (SOOS) Network Architecture for WebScale Data Centers

As discussed supra increased demand for cloud-based services can triggerbandwidth surges inside data centers, equivalent to 300 times the actualInternet traffic volume. Further, as discussed supra different trafficpatterns must be supported within Web Scale Data Centers (WSDC)including, but not limited to, persistent “elephant flows” andshort-lived delay sensitive “mice” flows. As noted more than 80% of theeast-west traffic bandwidth can be represented by “elephant flows”,which account for less than 10% of the number of flows, whereas “miceflows”, which account for 90% of the number of flows, represent lessthan 20% of the bandwidth. Within the industry optical switchingtechnology has been widely recognized as providing a solution to offload“elephant flows” from WSDC packet switched networks. However, prior artdesigns did not achieve high-bandwidth availability within a cost-viablescalable architecture.

Accordingly, the inventors have established an alternate architecture tothe prior art and their inventive MOS described supra in respect ofSection 2A. They refer to this as a Scaled Out Optically Switched (SOOS)network architecture for WSDC's. This architecture is based on opticalswitches containing several instances of silicon photonics planaroptical switches, e.g. 1×48, which are parallelized to support quadparallel lane optics to then enable switching on each lane. Use of large1×N switches avoids cascading smaller switches in a butterflyconfiguration. Further, by ensuring that there are no more than twooptical switch stages occur in the path of any circuit, low power singlemode silicon photonics transceivers can be used without requiringexternal amplification.

Referring to FIG. 7 there is depicted a SOOS data center networkarchitecture wherein the WSDC comprises 48 pods (Pod 1 810(1) to Pod 48810(48)) wherein each Pod n 810(n) comprises 48 racks (R1 to R48) with48 computer servers (C1 to C48) per rack resulting in 110,592 computerservers (48P×48R×48C=110,592C). As depicted in FIG. 8 the scaling out,amounting to 48P×48R×48C=110,592 C in total. Scaling out by way ofoptical switching is accomplished via 48 planes, Plane 1 820(1) to Plane48 820(48) each containing 12 optical switches, S #1 to S #12, forswitching between each rack, R, of each pod, P. The selection of a planeis accomplished via 12 optical switches (OS #1 to OS #12) inside eachpod, P.

Quad parallel lane pluggable optics (Q) such as 40 Gbps QSFP+ or 100Gbps QSFP28 expose each of the 8 lanes (L) (4 transmit lanes and 4receive lanes) on individual optical fibers through an eight-positionmulti-push-on (MPO) single mode connector. A single Q can be configuredas four individual full duplex transceivers at the 1/4 line rate (i.e.40/4=10 Gbps for QSFP+ and 100/4=25 Gbps for QSFP28). In order tosupport a scale out network architecture with transceivers containing 8L using a 1×48 switches (supporting 48 Top-of-Rack switches T(1) to T(4)within a single pod (P) and 48 pods (P) within a single WSDC), anefficient configuration for an Optical Switch (OS #n) is a Quad fullduplex design with 48 eight-position (for 8 lanes (L)) single modeconnectors. Inside the OS #n, 384 instances of 1×48 planar opticalswitches are interconnected by 4 fiber shuffles of 2304×2304 positions.

TABLE 1 Symbols and Quantities in SOOS Reference Network Architecture ofFIG. 8 Symbol Definition Total Quantity in SOOS WDC P Pod 48R R Rack 48P× 48R = 2304R T Top of Rack 48P × 48T = 2304T C Computer Server 48P ×48R × 48C = 110,592C S Optical Switch 576 − Intra · P − S + 576 − Inter· P − S = 1152S Intra P − S Intra-Pod Optical Switch 48P × 12S = 576 −Intra · P − S Inter P − S Inter-Pod Optical Switch 48P × 12S = 576 −Inter · P − S

Each rack (R) contains a Top of Rack switch (T(1) to T(48)), which isconnected to 12 optical switches (OS #1 to OS #12), within the same pod(P). Accordingly, within the pod (Pod 1 810(1) to Pod 48 810(48)) these12 optical switches (OS #1 to OS #12) perform the function of anintra-pod (intra-P) distributed optical fabric at the same hierarchicallevel as a spine switch within a prior art two-tier Leaf-Spine foldedClos network topology. In order to have enough resources to switch 12QPLPO per Top of Rack switch (T), which allows for 12 QPLPO*4 Lanes=48Lanes, allowing each Top of Rack switch (T) to have simultaneousconnectivity to all other top of rack switches within the same pod atthe 1/4 line rate of the QPLPO then 12 switches (OS #1 to OS #12) arerequired within each Pod n 810(n). Typically, within a given pod n810(n) the 12 optical switches might be located within a rack at themiddle of the pod and would connect to the 576 QPLPO evenly distributedacross the 48 Top of Rack (T) switches via MPO eight-fiber jumpers.

In an alternative embodiment, depicted in image 800 in FIG. 8, then theoptical switches may be integrated as a module within an Ethernet Top ofRack (ToR) switch, whereby a ToR may perform both Electronic PacketSwitched Leaf functionality as well as Optically Switched Spinefunctionality for other ToRs within the same Pod or local environment.

In the 48 pods (Pod 1 810(1) to Pod 48 810(48) of the entire WSDC, therewould be 48P×12S=576 intra P-S. Exploiting the SOOS architecture all 48pods of the WSDC are interconnected by 48 planes of inter-P opticalswitching, Plane 1 820(1) to Plane 48 820(48), wherein each planecomprises a further 12 optical switches (S #1 to S #12), for a total of48P×12S=576 inter P-S. The intra P-S switching is used to select theplane between any two pods there allowing any Top of Rack switch withina given Rack R in a given pod P n to be optically switched to anotherTop of Rack switch within another rack R within another P. The entireWSDC deployment would ultimately contain 576 intra-P S+576 inter-PS=1152 optical switches.

In an alternative embodiment, it would be evident to one skilled in theart that the number of optical planes can be reduced or increased as afunction of the Optical Switch radix to match the topology of the datacenter (i.e. radix of 64 for a WSDC of 64 planes across 64 pods of 64racks of 64 servers per rack, or radix of 32 for a WSDC of 32 planesacross 32 pods of 32 racks of 32 servers per rack).

Optical switching may be too slow for low latency “mice” flows andaccordingly SOOS provides a minimalistic 3-tier Leaf-Fabric-Spinenon-blocking Ethernet Packet Switches (EPS) 830 based on 1 QPLPO per Topof Rack (T), which is sufficiently large for all mice flows in the WSDC.In SOOS, 48 Ethernet Intra-P Fabric EPS 830 of 96 QPLPO and 48additional Ethernet Inter-P Spine EPS of 48 QPLPO are added to the 2304Top of Rack EPS for a total number of 2304+48+96=2400 Ethernet EPS.Consequently, to handle mice flows within the SOOS, there are(48×96Q)+(48×48Q)=6912 Q EPS ports in the Ethernet EPS Fabric-Spinetiers. By comparison, the 3+1 Posts 48R×48P prior art architecture ofFacebook, see for example(https://code.facebook.com/posts/360346274145943/introducing-data-center-fabric-the-next-generation-facebook-data-center-network/,is designed to include up to 64 fabric switches of 96 QSFP+ and up to192 fabric switches of 64 QSFP+, which amounts to(64×96Q)+(192×64Q)=18,432Q EPS ports in the Fabric-Spine tiers. Thusthis prior art design requires 18432/6912=2.7 times as many EPS ports asthe SOOS EPS Fabric-Spine tiers according to an embodiment of theinvention.

Within the SOOS according to an embodiment of the invention, in anygiven pod Pod (n) 810(n), each top of rack T has its uplink portsallocated as follows, 12 Q to 12 different intra-P S, 12 Q to 12 inter-PS as well as 1 Q to each of 48 different Ethernet Fabric EPS, for atotal of 25 Q. Each top of rack T of 32 Q, would thus have 32Q−25Q=7Qremaining for servers, which is enough for 7×4=28 computer servers C atthe 1/4 line rate per rack. Similarly, a top of rack T of 48 Q (of thesame size as the Spine EPS in SOOS), would have 48-25=23Q for 23 serversat the Q line rate and up to 23×4=92 computer servers C at the 1/4 linerate. Within SOOS only 3 T hops through the optical switches separateany two computer servers C across any two pods P, whereas in a 3-tierLeaf-Fabric-Spine, in addition to 2 T hops, there are 2 Fabric hops and1 Spine hop, for a total of 5 hops between any two computer servers Cacross any two pods P. Consequently, the latency due to EPS is decreasedwithin the inventive SOOS over a prior art 3-tier Leaf-Fabric-Spinearchitecture.

Within any given pod Pod n 810(n) of the exemplary SOOS architecturedepicted in FIG. 8, at the QSFP+ line rate, the total optically switchedbandwidth between all top of rack switches is 48T×12Q×40 Gbps=23,040Gbps on a 48 degree radix, thus the optically addressable capacity is23,040 Gbps×48 radix=1.1 Pbps (1.1 peta bits per second). At the QSFP28line rate, however, the bandwidth is 48T×12Q×100 Gbps=57,600 Gbps on a48 degree radix. The addressable capacity therefore is 57,600 Gbps×48radix=2.76 Pbps. Within the WSDC, the total number of transceivers inthe top of racks T connected to Intra-P S and Inter-P S, is 24×2304 T(24QperT)=55,296Q. Since each circuit has 1 Q at each end, at the QSFP28line rate, the total available bandwidth prior to optical switchingwould be (55296 Q/2)×100 Gbp 2.76 Pbps. This bandwidth is firstoptically switched on a 48-degree radix by all 576 Intra-P S opticalswitches and then optically switched again, on an additional 48-degreeradix by all 576 Inter-P S optical switches. The total resultingaddressable bandwidth across the entire WSDC is 2.76 Pbps×48×48=6,359Pbps s (intra-P+ inter-P). The entire WSDC has thus 6,359 Pbps/2.76Pbps=2,304 times as much optically switched bandwidth as simultaneousbandwidth. Referring to FIG. 8 there is depicted the growth in EPS portsand optical switching ports in the entire SOOS WSDC as a function of thescale out. It is shown that the sum of SOOS ports is significantlysmaller than the number of EPS ports of an alternative prior art WSDCdesign based upon a 3-tier Clos at the same sustained bandwidth asdescribed in SOOS.

3. Large-Scale Silicon Photonics MOEMS Integration for Optical Switches

3A: Optical Switch Concept

Within each MOS RNA 650 described with respect to FIGS. 6 through 8multiple 1:32 photonic optical switching devices are employed for thetransmitter side routing TxOS 740 optical engines and the receiver siderouting RxOS 770 optical engines. These exploit a micro-optic tunableswitch (MOTUS) core based upon novel MOEMS developed by the inventors.Referring to FIG. 9 first and second optical engines 900A and 900B aredepicted exploiting a tunable MOEMS for routing to/from N outputwaveguides from/to a single waveguide via a rotational MEMS mirror withthe mirror on the rear or front facets of the MEMS mirror respectively.As depicted in optical micrograph 900C and first micrograph 900D thetunable MEMS comprises a mirror section 930 wherein the curved MEMSmirror 930A turns relative to a planar waveguide region 930B to whichare coupled the channel waveguides. The curved MEMS mirror 930A iscoupled to a MEMS actuator 920 which rotates the curved MEMS mirror 930Aunder electrostatic actuation. To reduce power consumption the curvedMEMS mirror 930A may be latched into position using latching actuator910 which is depicted in detail in second micrograph 900E. The latchlock comprises a movable part as depicted in second micrograph 900E onboth sides of the latching moving into lock position whilst the latchmoves down. The actuator of the lock allows the latch to move freely upand down.

Alternate embodiments of 1×N optical switches without a mirror elementwithin the MOTUS are depicted and described below in respect of FIGS.20A and 20B. An alternate embodiment using a directional coupler, orother optical coupler, network rather than a second optical switch onthe combining stage of a circuit comprising multiple optical switches onthe same silicon die are depicted and described with respect to FIG.13B.

3B: Optical Waveguide Technologies

MOEMS and particularly MEMS mirrors and other MEMS actuators aretypically fabricated with the silicon as the substrate of choice due tothe availability of standard MEMS fabrication processes, prototypingfacilities, and production operations, e.g. MUMPs (Multi-User MEMSProcesses) from MEMSCAP, Sandia National Laboratories SUMMiT Vprocesses, Teledyne DALSA's Multi-Project Wafer “Shuttle” runs andproduction facilities, and STMicroelectronics high volume MEMSmanufacturing facilities for example.

3B.1: Silicon Nitride Waveguide Platform

Amongst the optical waveguide technology options for optical waveguidesin the telecommunication windows at 1300 nm and/or 1550 nm on siliconare silicon nitride (Si₃N₄) cored waveguides with silicon dioxide (SiO₂)cladding. An example of such a waveguide geometry is depicted in firstwaveguide cross-section 1000A in FIG. 10. Accordingly, the opticalwaveguide 1000 comprises a lower silicon dioxide 130 cladding, a siliconnitride (Si₃N₄) 140 core, and an upper silicon dioxide (SiO₂) 130cladding. The waveguide cross-section 1000A is depicted where an opticalwaveguide 1000 couples via an air gap to the MEMS mirror (MEMSM) 1100within a tunable component employing a MEMS element, such as the curvedMEMS mirror 930A relative to the planar waveguide region 930B. As theoptical waveguide is 10 μm thick the MEMSM 1100 at the air gap interfacemay be the same material structure atop an actuated silicon (Si) MEMSstructure formed within the Si substrate. The optical waveguide 1000 hasbelow it before the Si substrate a layer of polyimide which is etchedback to form part of the pivot for the MEMSM 1100. Deposited onto thevertical end wall of the optical waveguide 1000 and wall of the MEMSM1100 are anti-reflection coatings.

Now considering design guidelines for a Si₃N₄ waveguide based MEMSMwavelength tunable PIC circuit then consider a MEMS mirror design radiusof 1.00 mm, that the optical waveguides coupling to the Bragg reflectorsare spaced 200 μm away from the edge of the MEMSM, and that in eachinstance the distance from the pivot mounting of the MEMSM to theoptical waveguides is equal to the radius of the MEMSM. Accordingly, theresulting width of the MEMSM is 950 μm and considering a maximum angularrotation of the MEMSM as ±+3 then the lateral spacing between the upperand lower end waveguides is 105 μm respectively. Now considering 0.75 μmspaced waveguides the maximum number of channels accessible is 74 (+37channels from centre) at a design radius of 1.00 mm and at a smaller 0.5μm channel spacing it is 80 channels (+40 channels from centre).Accordingly, it would be evident that with a Si₃N₄ waveguide technologythat the number of channels can be significant. With different designparameters devices such as smaller MEMS mirror design radius deviceswith channel counts of 12, 16, 18, 24, 32, and 40, for example, may beimplemented within the ±+3 MEMS mirror rotation and smaller diefootprint. Accordingly, high channel count compact electro-staticallyactuated MEMS 1:N and N:1 optical switches with small footprint and lowpower consumption can be implemented upon a manufacturing platformsupporting integrated CMOS electronics and high volume low cost standardprocesses.

3B.2: Silicon on Insulator Waveguide Platform

Amongst the optical waveguide technology options for optical waveguidesin the telecommunication windows at 1300 nm and 1550 nm on silicon aresilicon-on-insulator waveguides with air cladding at the top and silicondioxide (SiO₂) cladding at the bottom. Such a platform is depicted insecond waveguide cross-section 1000B in FIG. 10 with a waveguidegeometry 1200 comprising a lower silicon dioxide (SiO₂) 130 lowercladding, a silicon 120 core, and relying on the refractive index of airor another material to form the upper cladding. The waveguidecross-section 1000B is similarly depicted where the optical waveguide1200 couples via the air gap to the MEMSM 1300, such as the curved MEMSmirror 930A relative to the planar waveguide region 930B.

However, due to the high refractive index of the Si 120 the thicknesslimit of the silicon (Si) for a single-mode waveguide is 220 nm which isgenerally too thin for MEMS devices. However, at a thickness of 5 modesexist within a silicon planar waveguide having modal indices of 1 μm andaccordingly a rib waveguide geometry may be employed in order to selectthe fundamental mode. Accordingly, the MEMSM 1300 for 1 μm Si may beformed from the same material. Due to the refractive indices theanti-reflection (AR) layer on the air gap of the optical waveguide 1200and MEMSM 1300 can be formed from parylene with a refractive index of1.66. The thickness of the AR coating would be approximately 233 nm.

Now considering design guidelines for a silicon-on-insulator waveguidebased MEMSM wavelength tunable PIC circuit then consider a MEMS mirrordesign radius of 2.00 mm, that the optical waveguides are spaced 200 μmaway from the edge of the MEMSM and the distance from the pivot mountingof the MEMSM to the optical waveguides is equal to the radius of theMEMSM. Accordingly, the resulting width of the MEMSM is 680 μm and,again, considering a maximum angular rotation of the MEMSM as ±3 thenthe lateral spacing between the upper and lower end waveguides is 209μm. Referring to FIG. 11 there is depicted the number of accessiblechannels for optical waveguides having spacings of 4.5 μm and 5.5 μmrespectively. Accordingly, for 5.5 μm spaced waveguides the maximumnumber of channels accessible is 74 (+37 channels from centre) at designradii of 2.00 mm whilst the corresponding maximum number of channelsaccessible for this design radii with 4.50 μm channel spacing is 90channels (+45 channels from centre).

Accordingly it would be evident that with a silicon-on-insulatorwaveguide technology similarly allows for a significant number ofchannels. With different design parameters devices such as smaller MEMSmirror design radius devices with channel counts of 12, 16, 18, 24, 32,40, and 64, for example, may be implemented within the ±3 MEMS mirrorrotation and smaller die footprint. Accordingly, high channel countcompact electro-statically actuated MEMS 1:N and N: 1 optical switcheswith small footprint and low power consumption can be implemented upon amanufacturing platform supporting integrated CMOS electronics and highvolume low cost standard processes.

3C: MOTUS Based MOS Optical Switch Modules

The dimensions of the novel silicon photonics based MOTUS 1: N (e.g.N=32) then the packaged component is not constrained by the footprint ofthe circuit, but rather by the space required by the N+1, e.g. 33,strands of optical fiber attached to the chip. The planar opticalcircuit chip is designed with N+1 high-quality v-grooves, making itpossible to attach, with low-loss, a large array of N+1 optical fibers.As a result of the large quantity of optical fibers attached to the samechip, a practical limit has been found in the packaging multiple, forexample four, instances of high N 1: N planar optical switches onto thesame chip. A fully silicon packaged chip, inclusive of four 1:32 planarMOTUS optical switches, measures less than 150 mm 2 and provides forenough space for the attachment of the required 4×(32+1)=132 strands ofoptical fiber. In contrast the MOTUS 4×(1:32) die itself is sufficientlysmall enough that over 200 chips can be made from a single 8-inch wafer.Wafer scale testing of the optical switches makes it possible to achievea cost per chip similar to what is possible in the microelectronicsindustry for other kinds of silicon chips such as integrated circuits.

Accordingly, it would be evident that such 1: N MOTUS optical enginesmay form the basis of the 1:32 TxOS 740 and 32:1 RxOS 770 within the 3URack Unit 710 modules 730A to 730D or 1U Rack Unit 720. However, furtherintegration using 16 “chips” with four 1:32 MOTUS switch instanceswithin each would allow a single printed circuit board to be packagedwith 64 fibers facing the ToR QSFP+ interfaces and 2048 fibers facingother modular optical switches. The resulting 64×2048 modular opticalswitch is compact enough with low power to support within a single datacenter rack unit configuration. The stacking of modular optical switchesis made possible through high-density fiber optical jumpers connectingtheir internal fiber shuffles together. The modularity of the opticalswitches makes it possible to deploy them coincidentally with additionalToRs at the time of commissioning new racks. Further, as these MOTUSoptical switches are low-power, low-cost, protocol agnostic, payloadagnostic, wavelength division multiplexing agnostic and avoid singlepoint of failures they support the upgrade of data rates through TDM andWDM.

3D: MOTUS Based Leaf and Spine Optical Switch Modules

The MOTUS optical engines described and depicted above for high N 1: Nand N:1 optical switches can also be applied to small N N×N opticalswitches such, for example, a 4×4 non-blocking building block using4-ary 2-fly switching methodology. As N=4 then more compact rotary MEMSelements may be employed within the MOTUS optical engines allowing afully integrated 4×4 matrix to be integrated into a 4 mm² die asdepicted in FIG. 12 with layout 1300A comprising a fully connectedswitch matrix such as depicted in schematic 1300B 4 1:4 optical switchesand 4 4:1 optical switches with fully connected optical interconnect.Accordingly, the 4×4 4 mm² die now has only 8 optical fiber connections.Such a 4×4 may form the basis of an optical switch module within a LeafSwitch. It would be evident that the fully connected switch matrixprovides strictly non-blocking routing and reconfiguration within such aLeaf Switch. The architecture may be generalized to N×N using 1:N andN:1 optical switches although with increasing N the waveguideinterconnect may be moved off-chip due to the complexities of routingthe N² cross-connect.

Accordingly, it is possible to consider an optical spine switch whereinan input array of 64×(1×64) input switches are coupled to 64×(64×1)output switches via a 64×64=4,096 fiber interconnection network. Such anoptical interconnect may exploit optical fiber and/or polymer flexibleplanar interconnection methodologies or exploit staked V-grooveinterconnections for a compact 64×64 cross-connect with the 64 outputsof a switch in an input V-groove coupled to an output V-groove array of64 V-groove assemblies at right angles.

Within optical switching applications according to embodiments of theinvention the likelihood of a transmitter within a node routing to aconnection that routes back to an associated receiver is low andaccordingly depicted in FIG. 12 in second schematic 1300C there isdepicted a reduced complexity (RC) N×N optical switch (RCOS) accordingto an embodiment of the invention. As depicted the RCOS employs N 1:(N−1) and (N−1): 1 switch matrices and having a (N−1)×(N−1)cross-connect. Accordingly, each input In #X(X=1, 2, 3, 4) may route toan output Out #Y(Y=1, 2, 3, 4)(Y≠X) with reduced complexity switchingand optical interconnect.

Now referring to FIG. 13 there are depicted 4×4 and 8×8 optical switchmatrices within first and second image 1300D and 1300E respectivelyaccording to embodiments of the invention employing and MOTUS opticalengines respectively in conjunction with directional coupler basedrouting to the optical receivers. First image 1300D depicts an 4×4optical switch comprising first to fourth MOTUS optical engines 1310A to1310D which are coupled to data sources, not shown for clarity, andselect an output port for transmission to a selected receiver of firstto fourth optical receivers 1320A to 1320D respectively under control ofa controller, not shown for clarity. Each output port from a MOTUSoptical engine 1310A to 1310D respectively is coupled via one or moredirectional couplers to the selected receiver. Due to the design of thecross-over matrix each optical path consists of horizontal and verticallinks to/from the directional couplers such that optical cross-oversbetween paths are 90 degrees for high crosstalk and low loss. However,the architecture also reduces the number of cross-connects when comparedto a conventional fully connected architecture.

In contrast, in second image 1300E extension of the design methodologyis presented for a 8×8 switch matrix wherein first to eighth pluggabletransceivers 1330A to 1330H are coupled to first to eighth MOTUS opticalswitches 1340A to 1340H and first to eighth receivers 1350A to 1350Hrespectively. The optical output of each first to eighth MOTUS opticalswitches 1340A to 1340H is coupled to a directional coupler basedrouting matrix and therein to the appropriate receiver of the first toeighth receivers 1350A to 1350H respectively. This configurationprovides for loop-back whereas if this feature is not required thematrix can be reduced to a multiple fiber interconnect. Again due to thedesign of the cross-over matrix each optical path consists of horizontaland vertical links from each MOTUS optical switch to a receiver via thedirectional couplers such that optical cross-overs between paths are 90degrees for high crosstalk and low loss. Again, the architecture alsoreduces the number of cross-connects when compared to a conventionalfully connected architecture.

Also depicted in FIG. 13 is a cross-over 1300F according to anembodiment of the invention such as implemented within the 4×4 and 8×8optical switch matrices within first and second images 1300D and 1300Erespectively in FIG. 13B. At the cross-over 1300F each optical waveguide1360 has a taper 1370 expanding the optical beam thereby improving theperformance of the cross-over 1300F. Within the tapers 1370sub-wavelength nanostructures may be formed to further improve theperformance of the cross-over by enhancing mode conversion to anexpanded beam. Accordingly, insertion loss may be reduced.

Notwithstanding the aforementioned 4×4 and 8×8 optical switch matricesemploying on-chip waveguide crossings, it would be apparent to oneskilled in the art that larger switch matrices may be designed at theexpense of additional crossings. For instances, a 48×48 design mayrequire about 95 perpendicular crossings in the path of any switchedposition, which at 0.01 dB/crossing would result in about 1 dB ofadditional on-chip losses due to crossings.

4. Time Dilated Spatial Switch Matrices

Within embodiments of the invention with respect to FIGS. 4 to 8 andFIG. 13 MOEMS based MOTUS optical switching engines provide a compact,low-power, low-cost, protocol agnostic, payload agnostic, and wavelengthdivision multiplexing agnostic technology for providing photonicswitching fabrics within Leaf-Spine routing structures within datacenters. Such MOEMS based MOTUS optical switching engines may also beemployed within other photonic switching fabrics such as the routers,wavelength add-drop multiplexers, protection switching, etc. However,the switching speed of these MOEMS based devices employing rotatingmirrors is of the order of 10 μs-100 us which in many applications maybe too slow due to the requirement that the optical link beingreconfigured is inactive during the switching process. Accordingly, theinventors have established time dilated spatial switch matrices ortemporospatial switch matrices. Referring to FIG. 14 there is depicted atemporospatial N×N switch 1400A employing first and second temporalswitching stages 1410 and 1440 in conjunction with central spatialswitching stage comprising first and second matrices 1420 and 1430.First and second temporal switching stages F1 1410 and F2 1440 compriseN×(1×2) and N×(2×1) switching arrays whilst first and second matricesSFM1 1420 and SFM2 1430 comprise N×N switching matrices.

Accordingly, as depicted by timing diagram 1400B optical traffic isinitially routed through first matrix SFM1 1420 until a time T whereinthe second matrix SFM2 1430 is triggered to the new desiredconfiguration. Accordingly, at T₂=T+T_(MEMS), where T_(MEMS) is theswitching time of the MOEMS switch, the second matrix SFM2 1430 isestablished and after a buffer period, T_(BUFFER), the first and secondtemporal switching stages F1 1410 and F2 1440 are triggered,T₃=T₂+T_(BUFFER)=T₁+T_(MEMS)+T_(BUFFER), such that atT₄=T₃+T_(FAST)=T₁+T_(MEMS)+T_(BUFFER)+T_(FAST), where T_(FAST) is theswitching speed of the first and second temporal switching stages F11410 and F2 1440 respectively, the new switching configuration isestablished and active for live traffic. If the first and secondtemporal switching stages F1 1410 and F2 1440 which are depicted asarrays of 1:2 and 2:1 switches are implemented using lithium niobatephotonic circuits then sub-nanosecond switching speeds can be achievedwith ease. According to the photonic circuit technology of the first andsecond temporal switching stages F1 1410 and F2 1440 switching speedsfrom microseconds to sub-nanosecond may be achieved. As such the MOEMSswitching time, T_(MEMS), defines the maximum rate of reconfiguration ofthe temporospatial N×N switch 1400A providedT_(MEMS)≤T_(ELAPSE)+T_(FAST), whilst the first and second temporalswitching stages F1 1410 and F2 1440 define the switching speed of thetemporospatial N×N switch 1400A.

Referring to FIG. 15 there is depicted an exemplary temporospatial N×Nswitch 1500 comprising first and second 4×4 spatial matrices 1520A and1520B together with first to fourth input 1×2 temporal switches 1510A to1510D respectively and first to fourth output 1×2 temporal switches1530A to 1530D respectively. Exploiting photonic circuit technologiesall 8 temporal switches may be integrated to a single die and both 4×4spatial matrices may be integrated to a single die and theseco-packaged. Alternatively, compound semiconductor InGaAsP switches withor without integrated optical amplification may be employed for thetemporal switches or as developments continue on silicon photonicspotentially the temporal and spatial switches may be formed within thesame silicon die.

The temporospatial N×N switch is generalized in temporospatial N×Nswitch 1550 in FIG. 15 wherein M N×N spatial switches 1570(1) to 1570(M)are depicted as being disposed between an input temporal switch 1560providing N channels of 1: M switching and output temporal switch 1580providing N channels of M:1 switching. In contrast to temporospatial N×Nswitch 1400A with only 2 spatial switching matrices the M spatialswitching matrices allow the temporospatial N×N switch 1550 toreconfigure at a rate faster than T_(MEMS) as, for example once a secondspatial N×N switch has been configured and active then rather than thetemporospatial N×N switch waiting for the first spatial N×N switch toreconfigure and be switched back for live traffic a third N×N switch mayalready be reconfiguring. Accordingly, the dimension M may beestablished in dependence upon the maximum reconfiguration rate and theswitching time of the spatial matrices, ignoring buffering delays suchas T_(ELAPSE) and the temporal switching time T_(FAST)

The temporospatial N×N switch (TSN2S) methodology according toembodiments of the invention may also be applied to rearrangeablenon-blocking switch fabrics as well as strictly non-blocking switchfabrics as depicted in FIG. 16 with first and second TSN2S matrices 1600and 1650 respectively employing a common 32×32 rearrangeable Benesnetwork employing 2×2 switching elements. Referring to first TSN2S 1600then this may be viewed as a degree-2 16×16 TSN2S employing first andsecond 16×16 spatial matrices 1620 and 1630 with input and outputtemporal matrices 1610 and 1640 of complexity 16×(2×2). Alternatively,as depicted in second TSN2S 1650 then this may be viewed as a degree-48×8 TSN2S employing first to fourth 8×8 spatial matrices 1670A to 1670Dwhich are disposed between first and second input temporal 16×(2×2)matrices 1660 and 1665 and first and second output temporal 16×(2×2)matrices 1670 and 1675. The first and second input temporal 16×(2×2)matrices 1660 and 1665 and first and second output temporal 16×(2×2)matrices 1670 and 1675 being coupled via a perfect shuffle and thesecond input temporal 16×(2×2) matrix 1665 and second output temporal16×(2×2) matrix 1675 being coupled to the first to fourth 8×8 spatialmatrices 1670A to 1670D via 2 perfect shuffle networks connecting theupper 8 2×2 switches to first and second 8×8 spatial matrices 1670A and1670B and the lower 8 2×2 switches to third and fourth 8×8 spatialmatrices 1670C and 1670D.

Accordingly, if the 32×32 rearrangeable Benes network is constructedwith fast switches for the first, second, sixth, and seventh ranks andslow switches for the third to fifth ranks of switches then it may bedeployed as either a degree-2 16×16 TSN2S or degree-4 8×8 TSN2S. Theseconfigurations are depicted alternatively in first and second schematics1700 and 1750 in FIG. 17 as alternating planes of switching. The firstand second input temporal 16×(2×2) matrices 1660 and 1665 and first andsecond output temporal 16×(2×2) matrices 1670 and 1675 may alternativelybe replaced by 8×(1×4) and 8×(4×1) input and output temporal matricesrespectively.

A degree-4 32×32 temporospatial switching fabric employing such 32×(1×4)and 32×(4×1) input and output temporal matrices is depicted in FIG. 18with first schematic 1800. However, in contrast to temporospatialswitching fabrics described above in respect of FIG. 14 to 17 whereinstrictly non-blocking or rearrangeable non-blocking matrices aredescribed explicitly or implicitly described as switched into useindividually based upon the temporal switches all operating together.However, in these scenarios the spatial matrix being established for thenext reconfiguration must be fully configured prior to the temporalswitches switching. However, this does not necessarily have to beoperated in such a manner. Alternatively, paths within the 4 32×32temporospatial switching fabrics 1820Y (Y=A, B, C, D) may be establishedin parallel with the temporal input and output switches 1810X operatingindependently of one another. Accordingly, as depicted with first tofourth 32×32 temporospatial switching fabrics 1820A to 1820Drespectively the paths may be established within the 32×32temporospatial switching fabrics concurrently and the next configurationfor reconfiguring paths established within another of the 32×32temporospatial switching fabrics. Accordingly, only the path or pathsreconfiguring must stop transmitting for the reconfiguration whereas inthe routing of all paths through a single temporospatial switchingfabric all paths must suspend transmission.

It would be evident that the temporospatial switching fabric such asdepicted in FIG. 18 may through increased complexity within the controlalgorithm perform periodic re-packing of the paths so that the multipleplanes employ the minimum number of switching elements thereby allowingincreased flexibility in establishing new optical paths withoutrequiring one or more existing paths be reconfigured at the same time.Alternate re-packing may, for example, seek to partition all routes to aparticular spatial switch plane or re-pack subsets of input ports todifferent predetermined spatial switch planes. It would be evident thatthe temporospatial switching fabric such as depicted in FIG. 18 may beemployed with strictly non-blocking spatial switch fabrics, wide sensenon-blocking spatial switch fabrics, rearrangeable non-blocking spatialswitch fabrics, and blocking spatial switch fabrics. Optionally, theplurality of spatial switching fabrics may be all the same or in otherembodiments of the invention different blocking levels of spatialswitching fabrics may be employed. Optionally, the input and outputtemporal switch arrays may be configurable in the wavelength domain suchthat particular ports are associated with specific wavelength(s).Optionally, some spatial switching fabrics may be of differentdimensions to others within the temporospatial switching fabric or mayexploit alternate technologies such that some planes of the plurality ofspatial switching fabrics route at different rates. For example, a MOEMS1:4 MOTUS optical engine with reduced angular rotation may be designedto switch faster than a MOEMS 1:32 MOTUS optical engine in the sametechnology. As such short burst “elephant” traffic may be routed throughsuch a spatial switching fabric due to the ability to reconfigure theplane faster than others. Optionally, traffic routed to this plane mayif the link exceeds a predetermined duration be routed onto anotherplane of the spatial switching fabrics. It would be evident that a rangeof configurations may be employed without departing from the scope ofthe invention.

Within the descriptions supra in respect of FIGS. 14 to 18 determinationwith respect to the configuration of the temporospatial switchingfabrics in respect of mapping input ports to output ports is implicitlydetermined by a controller. It would be evident that in embodiments ofthe invention that the controller may be provided by the mapping from aremote controller, e.g. within the data center, based upon signalingfrom the devices connected to the temporospatial switching fabric (e.g.the leaf switches), or based upon signaling from devices impacted bytraffic loading (e.g. spine switches wherein the temporospatialswitching fabric is connected to leaf switches). Alternatively, thenecessary control information for the temporospatial switching fabricmay be locally derived such as for example, by analysis of the signalsreceived, e.g. header/preamble data.

Within other embodiments of the invention the temporospatial switchingfabric may be employed in offloading network pipelines where the packetswitching layer is heavily loaded. Accordingly, the temporospatialswitching fabric may be a hybrid switch with both optical and packetswitch ports wherein these are then all routed optically but the packetswitch ports are routed to the packet switch rather than to local/remoteoptical interfaced equipment/network(s). Accordingly, it would bepossible to probe into the packet header in the switch pipeline deepbuffers, and identify from the header, prior to the payload hitting thetemporospatial switching fabric the configuration required for the nextpacket whilst the first packet is being transferred. Accordingly, theamount of dead time in transmitting could be reduced. Optionally, someplanes of the spatial switching within the temporospatial switchingfabric may be preferentially employed by the packet data.

Referring to FIG. 19 there is depicted an out of band synchronizationmechanism between a pair of optical circuit switches 1910 and 1920. Asdepicted each output of the first optical switch 1910 is coupled to thesecond optical switch via first, second, and third taps 1930, 1960, and1970 respectively. First taps 1930 couple X %, e.g. ×=2, to firstphotodetectors 1940. Coupled to each of the second taps 1960 are opticalsources 1950 such that Y %, e.g. Y=2, of the optical source 1950 outputis coupled onto the optical fibers with the optical signals from thefirst optical circuit switch 1910 to the second optical circuit switch1920. Each of these signals then passes through filters 1970 that couplethe output from the optical sources 1950 to second photodetectors 1980but pass the network signals directly to the second optical circuitswitch 1920. Accordingly, a control circuit, not shown for clarity,receives the outputs from the first photodetectors 1940 to determinewhich optical sources 1950 to enable and therein provide signals tosecond photodetectors 1980.

Accordingly, for example, the presence of an optical signal on theswitched channel from the first optical circuit switch triggers alloptical sources 1950 other than that associated with the active channelsuch the outputs of these optical sources 1950, which may for example beout of transmission band LEDs, are active and coupled through thefilters to the second photodetectors 1980 such that a second controlcircuit, also not shown for clarity, determines from the receivedsignals “‘all but those active” as the port it is to switch on. As suchthe second optical circuit switch 1920 may be switched based upon apreamble signal within the transmitted optical signals. Generally thefirst taps 1930 and first photodetectors 1940 would be removed and theoptical sources 1950 triggered based upon the control circuit knowingthe configuration of the first optical switch circuit 1910. In thismanner out of band signaling in the optical layer can be employed tosynchronise the first and second optical switch circuits 1910 and 1920respectively which may be geographically remote from one another. Whilstthe example depicted in FIG. 19 is simple it would be evident that theapproach applies to generalized switching fabrics as each inactive pathcarries an out of band signal such that these may be received atmultiple remote switches in combination with others to make thedetermination of the active path. Alternatively, only the active path islit with the out of band signal.

Optionally, the second taps 1960 may be multiplexers combining thetransmission signals with the out of band optical source 1950 signalsthrough coarse WDM. Such multiplexers may be integrated with the MOTUSoptical engine as may the first taps 1930 if implemented. Similarly, thefilters 1970, demultiplexers, may be integrated with the respectivesecond optical circuit switch MOTUS optical engine. Accordingly, a lowbitrate/continuous wave and ultra-low latency synchronization betweenoptical switches can be implemented with cheap LEDs and low costphotodiodes. Not only may the multiplexer and demultiplexers beintegrated with the silicon MOEMS but the photodetectors and LEDs mayalso be integrated to the silicon die using monolithic and/or hybridintegration techniques.

5. Enhanced MOEMS Optical Switching Devices

Within the preceding sections optical switching fabrics exploitingmicrooptoelectromechanical systems (MOEMS) have been described both withrespect to small switching fabrics, i.e. 4×4, distributive switchingelements, e.g. 1×48, and large switching fabrics. The inventors haveestablished within preceding patent applications many building blocks ofthese MOEMS optical switches, these patent applications including:

-   -   U.S. Provisional Patent Application 61/949,474 entitled “Mirror        Based MicroElectroMechanical Systems and Methods” filed Mar. 7,        2014;    -   World Intellectual Property Office Patent Cooperation Treaty        Application entitled “Mirror Based MicroElectroMechanical        Systems and Methods” filed Mar. 9, 2015;    -   U.S. Provisional Patent Application 61/950,238 entitled “Methods        and Systems Relating to Optical Networks” filed Mar. 10, 2014;    -   World Intellectual Property Office Patent Cooperation Treaty        Application entitled “Methods and Systems Relating to Optical        Networks” filed Mar. 10, 2015;    -   U.S. Provisional Patent Application 61/949,484 entitled “Methods        and System for Wavelength Tunable Optical Components and        Sub-Systems” filed Mar. 7, 2014; and    -   World Intellectual Property Office Patent Cooperation Treaty        Application entitled “Wavelength Tunable Optical Components and        Sub-Systems” filed Mar. 9, 2015.

Within the following Sections 5.1 to 5.3 variant optical switchesexploiting MOEMS technology are presented without the use of areflecting mirror such as employed in the MOTUS optical enginesdescribed and depicted supra in respect of 1×N optical switches.

5.1 Direct MOEMS M×N Optical Switches with Full and Half PositionLatching

Referring to FIG. 20A there is depicted a direct waveguide-waveguide 1×NMOEMS optical switch with pivoting waveguide and dual lateral latchingactuators. As depicted an input waveguide 2010 is formed upon region ofthe substrate which comprises the silicon substrate and interveninglayers together with the optical waveguide stack in a well-known priorart configuration of a waveguide on a substrate, what the inventorsrefer to as a non-suspended waveguide. This then transitions towaveguide portions 2020 and 2025 which are suspended waveguide portionsin that the substrate has been etched out below fully or leaving a thinlayer beneath the waveguide structure. Waveguide portions 2020 and 2025are before and after pivot point 2045 which is a pillar coupled to thewaveguide structure etched through the substrate, such as depicted inthird cross-section 2275 in FIG. 22A. Laterally coupled to the beamsupporting the optical waveguide portions 2020 and 2025 via beams arefirst and second rotary actuators 2040 and 2050. These underelectrostatic forces generated through application of appropriate DCvoltages to the first and second rotary actuators 2040 and 2050 twistthe waveguide beam on its pillar about the pivot point 2045 such thatthe end of the optical waveguide can be aligned to the desired opticalwaveguide of the array of optical waveguides 2070 that are disposed upona second non-suspended portion of the MOEMS structure.

Once rotated the first and second actuators 2040 and 2050 can be latchedinto position by either the first and second latching actuators 2030 and2060 respectively thereby allowing the switch to be maintained inselected configuration without continued application of the DC voltagesto the first and second rotary actuators 2040 and 2050 respectively. Byoffsetting the latching angles of, for example, second latching actuator2060 at half the step of the first latching actuator 2030 then angularresolution can be increased for the latched position allowing the numberof settable positions to be doubled thereby allowing either increasednumber of waveguides and/or lower rotation angle ranges. Accordingly,the MOEMS optical switch within FIG. 20A functions as a latchable 1×Noptical switch where N is the number of addressable/provided waveguideswithin the array of optical waveguides 2070. It would be evident thatalternatively the optical switch functions as a latchable N×1 opticalswitch by reversing the associations of waveguides as input and outputs.

Now referring to FIG. 20B there is depicted essentially the samemechanical configuration as that depicted within FIG. 20 except that nowthe non-suspended input waveguide section 2080 has M optical waveguidesas do the suspended waveguide portions 2090 and 2095 such that therotation of the beam under the action of the first and second rotaryactuators 2040 and 2050 now aligns the M optical waveguides to a subsetof the N output waveguides within the array of optical waveguides 2070or if these are at different pitches a selected one or subset of the Moptical waveguides to a subset of the N output waveguides. For example,rotation in one direction aligns the M optical waveguides to one subsetof the N output waveguides, e.g. M, where N=2×M, and when the rotationis in the other direction it aligns the M optical waveguides to anothersubset of the N output waveguides, e.g. M, where N=2×M. In this mannerthe optical switch depicted within FIG. 20B functions as M ganged 1×2optical switches or M ganged 2×1 optical switches. It would be evidentthat other configurations such as ganged 1×4 or 1×8 switches, forexample, may be implemented.

In order for the suspended beam with the waveguide(s) to rotate relativeto the array of optical waveguides 2070 an air gap is provided. However,as evident to one skilled in the art the air gap increases optical losseven at dimensions of 1-3 μm. Accordingly, referring to FIG. 20C thereis depicted a variant of the 1×N or M: N optical switches depicted inFIGS. 20A and 20B respectively. Accordingly, the suspended opticalwaveguide 2000A between the pivot point 2045 and array of waveguides2070 is now shaped with a flexible gap closing structure allowing thegap losses to be minimized as the structure through stresses within thecurved design seeks to reduce these and lengthen thereby bringing therotating waveguide(s) into contact with the array of output waveguides2070. Optionally, the flexible gap closing structure may be metallizedsuch that heating increases stresses inducing additional flexureallowing the gap to be made prior to moving the MOEMS and then releasedsubsequently. Due to the isolated nature of the suspended beam thethermal mass is low. Alternatively, the MOEMS may include a linearactuator to withdraw the waveguide(s), allow it (them) to be rotated andthen re-close the gap wherein the flexible gap closing structure absorbsover-run in the linear actuator.

5.2 MOEMS 2×2 Optical Switch for Crossover Free Crossbar Topologies

Within the preceding architectures described and discussed a significantportion exploit 1×N and N×1 optical switches, e.g. FIGS. 4-8B, 13, and15, although others exploit 2×2 switching elements, such as depictedwithin FIGS. 16-18. Whilst a 2×2 switching element can be implementedwith 4 1×2 switching elements with a passive interconnection this canlead to long building blocks for larger switch fabrics such thatgenerally architectures employing 1×2 switching elements tend to favourfully connected architectures such as depicted in FIG. 13 rather thancrossbar architectures such as depicted in FIG. 21A for example. Thestrictly non-blocking 4×4 crossbar depicted in FIG. 21A employs 16 2×2optical switches or 64 1×2 if these are implemented as the 2×2 buildingblocks. In contrast the fully connected requires only 24 1×2 but doesrequire a significant number of waveguide intersections unlike thecrossbar architecture. Further referring to FIG. 21B there are depicted4×4 matrix 2100D, 8×8 matrix 2100E, and 64×64 crossbar matrix 2100F allexploiting a 2×2 MOEMS switching elements 2100B such as described belowin respect of FIGS. 22A to 26B according to embodiments of theinvention. As evident from FIG. 21B 4×4 matrix 2100D which employs 162×2 MOEMS switching elements 2100B forms a “building block” within 8×8matrix 2100E such that 4 4×4 matrices 2100D are employed comprising atotal of 64 2×2 MOEMS switching elements 2100B. Each 8×8 matrix 2100Ethen becomes a “building block” such that 64 8×8 matrices 2100E form64×64 crossbar matrix 2100F thereby employing 1,296 2×2 MOEMS switchingelements 2100B.

Accordingly, the inventors have established in FIG. 22A with first image2200A a MOEMS 2×2 through provisioning of 1×2 evanescently coupledoptical elements (ECOEs). As depicted within first to fifthcross-sections 2260 to 2290 in second image 2200B the 1×2 ECOE employsin various regions:

-   -   Anchored MEMS structures (first cross-section 226) wherein the        upper silicon (Si) 2220 is anchored to the silicon (Si) 2220        substrate via the intermediate silicon dioxide (SiO₂) 2230        sacrificial layer;    -   Unanchored MEMS structures (second cross-section 2270) wherein        the SiO₂ 2230 and Si 2220 substrate have been etched and removed        leaving the Si MEMS element free-standing;    -   Pivoted suspended waveguide (third cross-section 2275) wherein a        SiO₂ 2230 clad and silicon nitride (Si₃N₄) core optical        waveguide sits atop a Si 2220 beam which has an isolated pillar        to the substrate (the pivot);    -   Suspended waveguide (fourth cross-section 2280) wherein a SiO₂        2230 clad and silicon nitride (Si₃N₄) core optical waveguide        sits atop a free Si 2220 beam; and    -   Non-suspended waveguide (fifth cross-section 2290) wherein a        SiO₂ 2230 clad and silicon nitride (Si₃N₄) core optical        waveguide is anchored to the silicon (Si) 2220 substrate via the        intermediate silicon dioxide (SiO₂) 2230 sacrificial layer.

Thin Si₃N₄ core layers, e.g. 70 nm≤t≤220 μm, may be employed wherepolarization independent operation is not required whilst in otherembodiments of the invention thicker Si₃N₄ core layers may be employed,t≈1 μm, for polarization independent switching operation. The operationof the 1×2 ECOE is depicted in FIGS. 23A and 23B respectively for the“default”, “bar” and “cross” states respectively. However, FIG. 22Bdepicts a 2×2 butt coupled optical element (BCOE) 2200A exploitingsimilar waveguide-waveguide coupling, commonly referred to buttcoupling, as the preceding embodiments of optical switches. In principlethe 2×2 BCOE switching element according to an embodiment of theinvention exploiting MOEMS elements operated in the same manner as the2×2 ECOE but with end-end waveguide coupling rather than evanescentcoupling. Considering initially first image 2300A in FIG. 23A then asuspended waveguide structure 2360 is depicted in-line withnon-suspended waveguide structures 2350. Each non-suspended waveguidestructure 2350 having a pair of waveguides representing the inputwaveguide pair or output waveguide pair. The suspended waveguidestructure 2360 comprises four optical waveguides, labelled 1-4, runningfrom one end to the other with one isolated and the other three crossingeach other in a predetermined pattern. The suspended waveguide structure2360 is coupled to MEMS 2340 which is a linear comb actuator withflexible anchors 2330 at either end and is disposed between first andsecond fixed combs coupled to V_(DD2) 2310 and V_(DD1) 2320. As depictedin first image 2300A in FIG. 23A with neither of the two voltagesV_(DD1) and V_(DD2) applied such that the MEMS 2340 is in a “neutral”default state.

Now referring to second image 2300B in FIG. 23B the appropriate voltagesV_(DD1) and V_(DD2) have been applied such that the MEMS 2340 andsuspended waveguides 2360 are moved such that waveguides 1 and 4 are nowevanescently coupled to the input and output waveguides by virtue of thewaveguides 1 and 4 being physically abutted to the projected suspendedportions of the input and output waveguides on the non-suspendedwaveguide structures 2350. Accordingly, the input and output waveguidesare coupled in the “bar” state via waveguides 1 and 4. Within thirdimage 2300C in FIG. 23C the appropriate voltages V_(DD1) and V_(DD2)have been applied such that the MEMS 2340 and suspended waveguides 2360are moved such that waveguides 2 and 3 are now evanescently coupled tothe input and output waveguides by virtue of the waveguides 2 and 3being physically abutted to the projected suspended portions of theinput and output waveguides on the non-suspended waveguide structures2350. Accordingly, the input and output waveguides are coupled in the“cross” state via waveguides 2 and 3. As such the 2×2 switching elementsupports both bar and cross states as well as a non-switched stateblocking the outputs from the inputs.

An alternate 2×2 switching element is depicted in FIG. 24 in first andsecond states 2400A and 2400B respectively according to an embodiment ofthe invention exploiting MOEMS elements and optical evanescent coupling.In first state 2400A the 2×2 switching element comprises a pair of MEMSactuators that are in first and second MEMS positions 2410A and 2420Athat control the motion of first and second suspended waveguide portions2430 and 2440 such that they are decoupled from the first and secondwaveguides 2450 and 2460 which cross-over in the middle of the device.Accordingly, with the first and second suspended waveguide portions 2430and 2440 decoupled the 2×2 switching element is in a defaultcross-state. In second image 2300B the MEMS actuators have been actuatedinto first and second MEMS positions 2410B and 2420B such that first andsecond suspended waveguide portions 2430 and 2440 are now a coupled tothe first and second waveguides 2450 and 2460 such that optical signalscoupled to the 2×2 switching element are evanescently coupled to thefirst and second suspended waveguide portions 2430 and 2440 propagatewithin and then re-couple back. In this manner the optical signalswithin first and second suspended waveguide portions 2430 and 2440bypass the cross-over in the middle of the device thereby putting the2×2 switching element into the bar-state. Optionally, the centralportion of the non-suspended waveguide portion of the design with thewaveguide cross-over and the optical waveguides coupling to/from thestructure may be designed such that the first and second suspendedwaveguide portions 2430 and 2440 form zero-gap directional couplers ordefined gap directional couplers wherein the waveguides upon thenon-suspended waveguide portion transition away within the centralportion to remove potential re-coupling back prior to the cross-overthereby leading to increased crosstalk.

5.3 Latching MOEMS 2×2 Optical Switch for Crossover Free CrossbarTopologies

Now referring to FIGS. 25A and 25B there is depicted a latching 2×2switching element according to an embodiment of the invention exploitingMOEMS elements and optical evanescent coupling in “cross” and “bar”states respectively such as described supra in respect of FIG. 24.Accordingly, the default cross-state of the 2×2 switching element is setby the waveguide cross-over within the non-suspended waveguide portion2510. Whilst the suspended waveguide portions 2530 may be moved underlinear actuator control from actuators 2510 to transition the 2×2switching element into the bar state by bring the suspended waveguideportions 2530 into predefined spacing relative to the non-suspendedwaveguide portion 2510 or back to the cross state by separating thesuspended waveguide portions 2530 from the non-suspended waveguideportion 2510 in either state first to fourth latches 2540A to 2540D incombination with springs 2520 maintain the switch in a defined state bylatching the suspended waveguide portions 2530 into position in eachswitch state. Springs 2520 act to pull the suspended waveguide portion2530 against the latches 2540A to 2540D. Also depicted are limiters 2560that limit motion of the suspended waveguide portions when the switch isplaced into the bar state. These limiters 2560 setting the waveguidespacing between the suspended waveguide portion 2530 and non-suspendedwaveguide portion 1310 to that established in coupling mode theory for100% power coupling between the waveguides by the time they re-separatefrom the “coupling” region.

Now referring to FIGS. 25C and 25D there is depicted a latching 2×2switching element according to an embodiment of the invention exploitingMOEMS elements and optical evanescent coupling in “cross” and “bar”states respectively such as described supra in respect of FIG. 24 andFIGS. 25A and 25B respectively. Accordingly, the default cross-state ofthe 2×2 switching element is set by the waveguide cross-over within thenon-suspended waveguide portion 2510 which is held at ground potential.Whilst the suspended waveguide portions 2530 may be moved under linearactuator control from actuators 2510 to transition the 2×2 switchingelement into the bar state by bring the suspended waveguide portions2530 into predefined spacing relative to the non-suspended waveguideportion 2510 or back to the cross state by separating the suspendedwaveguide portions 2530 from the non-suspended waveguide portion 2510 ineither state first to fourth latches 2540A to 2540D in combination withsprings 2520 maintain the switch in a defined state by latching thesuspended waveguide portions 2530 into position in each switch state.Springs 2520 act to pull the suspended waveguide portion 2530 againstthe latches 2540A to 2540D in the bar-state depicted in FIG. 25D andpush the suspended waveguide portion 2530 against the latches 2540A to2540D in the cross-state depicted in FIG. 25C. As indicated thesuspended waveguide portions 2530 are actuated via V_(DD1) applied tothe fixed portion of the MEMS actuators and the latches 2540A to 2540Dactuated via V_(DD2) again applied to the fixed portion of the MEMSactuators.

5.4 Latching Actuator-Less MOEMS 2×2 Optical Switch for Crossover FreeCrossbar Topologies

Within the preceding structures MEMS actuators have moved one or moreelements of a MOEMS optical switch in order to transition the opticalswitch from one switch state to another. However, referring to FIGS. 26Aand 26B there is depicted an alternate MEMS optical switch exploitingelectromagnetic force induced between the non-suspended waveguide 1330and suspended waveguide 1350 portions. Accordingly, in FIG. 26A thedefault cross-state of the 2×2 switching element is again set by thewaveguide cross-over within the non-suspended waveguide portion 1330when the suspended waveguide portions 1350 have been separated under theaction of the springs 1340 and then latched using first to fourthlatches 2540A to 2540D. However, when the first to fourth latches 2540Ato 2540D are released electromagnetic attraction between thenon-suspended waveguide portion 1330 and the suspended waveguideportions 1350 can be established pulling them towards the non-suspendedwaveguide portion 1330. Again, limiters 2660 act to limit the motion ofthe suspended waveguide portions 1350 such that the gap between thewaveguides is that established by coupling mode theory for 100% powercoupling between the waveguides by the time they re-separate from the“coupling” region. Electromagnetic attraction of the suspended waveguideportions 1350 can be established by appropriate biasing the suspendedwaveguide portion 1350 relative to the non-suspended waveguide portion1330.

5.5 Latching Actuator-Less MOEMS 2×2 Optical Switch for Crossover FreeCrossbar Topologies Using Passivation Layer as Spacer

Now referring to FIG. 27 there are depicted first and secondcross-sectional views 2700C and 2700D of embodiments of a latchingactuator-less MOEMS 2×2 optical switch 2700 according to an embodimentof the invention. Latching actuator-less MOEMS 2×2 optical switch 2700exploits a similar design and structure as that depicted by the MOEMSoptical switch in FIGS. 26A and 26B respectively exploitingelectromagnetic force induced between the non-suspended waveguide andsuspended waveguide portions. However, the latching actuator-less MOEMS2×2 optical switch 2700 does not employ limiter structures 2660 as italternatively relies upon direct physical abutment of the suspendedwaveguide portions 1350 and non-suspended waveguide portion 1330. InFIG. 27 the upper region 2700A is depicted in “disengaged” state wherethe suspended waveguide 1330 has been pulled away from the non-suspendedwaveguide 1350 by the spring alone or in combination with repulsion bychanging the polarity of the isolated suspended silicon whilst in lowerregion 2700B it is depicted in “engaged” state where the suspendedwaveguide 1330 has been engaged against the non-suspended waveguide 1350by electrostatic attraction against the spring force.

In first cross-section 2700C the Si₃N₄ core—SiO₂ cladding atop thesilicon 2220 is over-hanging on each of the suspended waveguides 1330and non-suspended waveguide 1350. In second cross-section 2700D theSi₃N₄ core—SiO₂ cladding atop the silicon 2220 is over-hanging on eachof the suspended waveguides 1330 but under-hung on the non-suspendedwaveguide 1350. It would be evident that other variants may beimplemented without departing from the scope of the invention.

Within FIG. 22A to 27 waveguide cross-overs are depicted as simplelinear junctions between the two waveguides. However, within embodimentsof the invention these cross-over regions may exploit beam formingthrough shaped waveguide transitions, mode coupling via sub-wavelengthstructures, etc. to enhance the crosstalk and loss performance of thecross-overs. It would also be evident that the performance of thedirectional couplers either zero-gap or fixed gap, will requiretailoring to the wavelength range of the optical switching network.

6. Vertical Directional Coupler Based MOEMS Optical Switching Elements

Within the descriptions supra in respect of FIG. 21B to 27B respectivelyoptical switching elements exploiting MOEMS activated lateraldirectional coupler elements have been described and depicted. However,the inventors have also established directional coupler elementsexploiting linear MOEMS motion with vertical directional couplers ratherthan lateral directional couplers. For example, referring to FIG. 28Athere are depicted first to fourth cross-sectional views 2800A to 2800Dof linear motion MOEMS based vertical optical coupling elementsaccording to embodiments of the invention. These being:

-   -   First cross-sectional view 2800A wherein the linear motion of a        suspended and translating MOEMS element with an optical        waveguide formed atop and overhanging allows the optical signals        to couple evanescently from the fixed optical waveguide to/from        the MOEMS optical waveguide and the linear translation motion        longitudinally alone or in combination with vertical translation        adjusts/stops the evanescent coupling;    -   Second cross-sectional view 2800B wherein the linear motion of        the suspended and translating MOEMS element with an optical        waveguide formed atop and overhanging allows the optical signals        to couple evanescently from the fixed optical waveguide to/from        the MOEMS optical waveguide and linear lateral motion alone or        in combination with vertical translation adjusts/stops the        evanescent coupling;    -   Third cross-sectional view 2800C wherein the linear motion of        the suspended and translating MOEMS element with an optical        waveguide formed atop and overhanging allows the optical signals        to couple evanescently to and from fixed optical waveguides        either end of the MOEMS element; and    -   Fourth cross-sectional view 2800D wherein the linear motion of        the suspended and translating MOEMS element with an optical        waveguide formed atop allows the optical signals to butt couple        to and from fixed optical waveguides.

It would be evident that within alternate embodiments of the inventionthat the translating element may be the lower waveguide of the verticaldirectional coupler rather than the upper waveguide as depicted in firstto third cross-sections 2800A to 2800D respectively. In thirdcross-sectional view 2800C translation of the central waveguide providesa different configuration of switching functionality to that where thecentral waveguide is fixed and input and/or output waveguides are movedtogether or independently. Now referring to FIG. 28B there are depictedfirst to third cross-sectional views 2850A to 2850C of rotary motionMOEMS based vertical optical coupling elements according to embodimentsof the invention. These being:

-   -   First cross-sectional view 2850A wherein the rotary motion of a        suspended MOEMS element with an optical waveguide formed atop        and overhanging allows the optical signals to couple        evanescently from the fixed optical waveguide to/from the MOEMS        optical waveguide and the rotary motion alone or in combination        with vertical translation adjusts/stops the evanescent coupling;    -   Second cross-sectional view 2850B wherein the rotary motion of        the suspended MOEMS element with an optical waveguide formed        atop allows the optical signals to couple through butt-coupling        of the fixed optical waveguide to/from the MOEMS optical        waveguide and rotary motion alone or in combination with        vertical translation adjusts/stops the coupling;    -   Third cross-sectional view 2800C wherein the rotary motion of        the suspended MOEMS element with an optical waveguide formed        atop and overhanging allows the optical signals to couple        evanescently to and from fixed optical waveguides in the aligned        configuration but rotation of the upper waveguide results in        coupling being stopped.

It would be evident that within alternate embodiments of the inventionthat the rotating element may be the lower waveguide of the verticaldirectional coupler rather than the upper waveguide as depicted in firstto third cross-sections 2850A to 2850C respectively.

7. Blocking 2×2 Unit Cells and Switch Matrices Exploiting Same

Now referring to FIG. 29A there is depicted in first schematic 2900A an1×2 optical switching element according to an embodiment of theinvention employing an optical switch supporting coupling in a firststate of inputs 2/1 to outputs 4/3 respectively and in a second staterouting from input 2 to output 3. Such an 1×2 element may then form thebasis of a range of M×N optical switch matrices such as the 4×4 and 3×4optical switch matrices depicted in second and third schematics 2900Band 2900C respectively. Referring to FIG. 29B there is depicted a linearmotion MOEMS based 1×2 optical switching element exploiting the topologydepicted in FIG. 29A for the 1×2 switching element according to anembodiment of the invention. As depicted first and second MEMS actuators2940 and 29560 respectively provide lateral motion (X-axis) of asuspended MOEMS platform including curved waveguide 2920 and crossover2910 whilst third MEMS actuator 2950 provides for movement of thesuspended MOEMS platform in the Y-axis.

Accordingly, the waveguides 2970 and 2980 are either coupled to thecurved waveguide 2920 or to the straight waveguides and therein thecrossover 2910. Accordingly, the MEMS actuators allow the MOEMS based1×2 optical switching element to be configured as depicted in firstschematic 2900A in FIG. 29A into State 1 and State 2. These states beingdepicted schematically in first and second schematics 3000A and 3000Brespectively wherein the linear motion MOEMS based 1×2 optical switchingelement depicted in FIG. 29B according to an embodiment of the inventionmay exploit linear butt-coupling in bar and cross-states wherein thewaveguides are shown with a gap for clarity such as depicted in respectof fourth schematic 2800D in FIG. 28A or vertical coupling such asdepicted in first schematic 2800A in FIG. 28A,

Now referring to FIG. 31 there are depicted 2×2 and 3×3 opticalswitching circuits 3100A and 3100B respectively according to anembodiment of the invention exploiting linear motion MOEMS based 1×2optical switching element according to FIGS. 29B and 30. The outerwaveguide paths of the 1×2 optical switching element pairs 3010A/3010Band 3010C/3010D in the 2×2 optical switching circuit 3100A are coupledvia waveguide mirrors 3030. Similarly, within the 3×3 optical switchingcircuit 3100B the 1×2 optical switching element pairs 3020A/3020B;3020B/3020C; 3020G/3020H; and 3020H/3020I are similarly coupled bywaveguide mirrors 3030. However, now referring to FIG. 32 there isdepicted an 8×8 optical switching matrix exploiting linear motion MOEMSbased first and second 1×2 optical switching elements 3210 and 3220 suchas depicted in FIGS. 29B and 30 according to an embodiment of theinvention wherein second 1×2 optical switching elements 3220 is aninverted design of first 1×2 optical switching elements 3210.Accordingly, the optical signals input at any input are coupled to theirrespective output ports by a single MOEMS activation and the opticalswitch matrix operates in a Path Independent LOSS (PILOSS)configuration.

Now referring to FIG. 33 there is depicted a rotary motion MOEMS based2×2 blocking optical switching element according to an embodiment of theinvention which performs similar routing as that depicted within FIG.29B. Accordingly, a rotary MOEMS element 3310 rotates such that thecircular section rotates around its center of rotation coupling thewaveguides on it with the inputs, I/P 1 and I/P 2, and outputs O/P 1 andO/P 2. Disposed upon the rotary MOEMS element 3310 are first to thirdwaveguides WG1, WG2, and WG3 respectively. Accordingly, the connectivityof the rotary motion MOEMS based 2×2 optical switching element is givenby Table 2 below.

TABLE 2 Connectivity of Rotary Motion MOEMS based 2 × 2 OpticalSwitching Element Configuration Input Link Output A I/P 1 WG 1 O/P 1 I/P2 WG 3 O/P 2 B I/P 1 WG 2 O/P 2 I/P 2 N/C N/C C I/P 1 N/C N/C I/P 2 WG 2O/P 1

Now referring to FIGS. 34 and 35 there are depicted schematics of arotary motion MOEMS based 1×5 optical switching element according to anembodiment of the invention. As depicted in FIG. 34 the electricalconnections to the MOEMS are:

-   -   Latch lock pad 3410;    -   Latch pad 3420;    -   Rotate clockwise pad 3430;    -   Gap closing pad 3440;    -   Rotate counter clockwise pad 3450; and    -   Ground 3460.

Referring to FIG. 35 the rotary motion MOEMS based 1×5 optical switchingelement is depicted coupled to the first and third waveguidesrespectively in first and second schematics 3500A and 3500Brespectively. Now referring to FIG. 36 there are depicted first andsecond electro-static gap closing schematics within a rotary motionMOEMS based 1×5 optical switching element according to an embodiment ofthe invention and as compatible with other rotary motion MOEMS basedoptical switching elements and circuits. In first schematic 3600A thesuspend and rotating MOEMS element and fixed MOEMS element are uncharged(or may be similarly charged) when the rotating MOEMS element may bemoved relative to the fixed MOEMS element. In contrast, in secondschematic 3600B the rotating and fixed MOEMS elements are oppositelycharged such that they are attracted to each other.

Referring to FIG. 37 there is depicted a variant of electro-static gapclosing is depicted compatible with linear or rotary motion MOEMS basedoptical switching elements according to an embodiment of the invention.In contrast to the configuration depicted in FIG. 36 the fixed elementsilicon has been etched such that the profile of the silicon is slopedsuch that as the rotating/linear element translates the opticalwaveguide structure is raised, if it has dropped, to the same level asthe optical waveguide on the fixed element.

Specific details are given in the above description to provide athorough understanding of the embodiments. However, it is understoodthat the embodiments may be practiced without these specific details.For example, circuits may be shown in block diagrams in order not toobscure the embodiments in unnecessary detail. In other instances,well-known circuits, processes, algorithms, structures, and techniquesmay be shown without unnecessary detail in order to avoid obscuring theembodiments.

The foregoing disclosure of the exemplary embodiments of the presentinvention has been presented for purposes of illustration anddescription. It is not intended to be exhaustive or to limit theinvention to the precise forms disclosed. Many variations andmodifications of the embodiments described herein will be apparent toone of ordinary skill in the art in light of the above disclosure. Thescope of the invention is to be defined only by the claims appendedhereto, and by their equivalents.

Further, in describing representative embodiments of the presentinvention, the specification may have presented the method and/orprocess of the present invention as a particular sequence of steps.However, to the extent that the method or process does not rely on theparticular order of steps set forth herein, the method or process shouldnot be limited to the particular sequence of steps described. As one ofordinary skill in the art would appreciate, other sequences of steps maybe possible. Therefore, the particular order of the steps set forth inthe specification should not be construed as limitations on the claims.In addition, the claims directed to the method and/or process of thepresent invention should not be limited to the performance of theirsteps in the order written, and one skilled in the art can readilyappreciate that the sequences may be varied and still remain within thespirit and scope of the present invention.

What is claimed is:
 1. A device comprising an optical switch matriximplemented on a MOEMS die comprising: a plurality of inputs andoutputs; a plurality of unit cells, each unit cell comprising: a MEMSactuated suspended waveguide platform incorporating a waveguide andanother waveguide which form a crossover where an end of the waveguideis disposed at a first predetermined location on the MEMS actuatedsuspended waveguide platform, an end of the another waveguide isdisposed at another first predetermined location on the MEMS actuatedsuspended waveguide platform; a curved waveguide where one end of thecurved waveguide is disposed at a second predetermined location on theMEMS actuated suspended waveguide platform proximate the firstpredetermined location of the end of the waveguide and a second distalend of the curved waveguide is disposed at another second predeterminedlocation on the MEMS actuated suspended waveguide platform proximate theanother first predetermined location of the end of the anotherwaveguide; a further waveguide disposed upon a first predeterminedportion of a MEMS actuator where the further waveguide has an enddisposed at a predetermined location on the MEMS actuator; an additionalwaveguide disposed upon a first predetermined portion of another MEMSactuator where the additional waveguide has an end disposed at apredetermined location on the another MEMS actuator; and a further MEMSactuator to linearly translate the MEMS actuated suspended waveguideplatform such that the MEMS actuated suspended waveguide platform movesrelative to the MEMS actuator and the another MEMS actuator; wherein aseparation of the first predetermined location of the end of thewaveguide and the second predetermined location of the end of the curvedwaveguide is the same as another separation of the first predeterminedlocation of the end of the another waveguide and the secondpredetermined location of the distal end of the curved waveguide; in afirst position the further MEMS actuator positions the MEMS actuatedsuspended waveguide platform such that the further waveguide is coupledto the second distal end of the curved waveguide and the additionalwaveguide is coupled to the end of the curved waveguide; and in a secondposition the further MEMS actuator positions the MEMS actuator suspendedwaveguide such that the further waveguide is coupled to the end of theanother waveguide and the additional waveguide is coupled to the end ofthe waveguide.
 2. The device according to claim 1, wherein the opticalswitch is an N×N optical switch matrix implemented on the same MOEMS diecomprising: an array of unit cells comprising a grid of N rows and Ncolumns; a plurality of N inputs each coupled to a unit cell in thefirst column; a plurality of N outputs each coupled to a unit cell inthe final column; wherein each unit cell in the top row routes an inputsignal either to the unit cell in the next column but same row or theunit cell in the next column and the row below; each unit cell in thebottom row routes an input signal either to the unit cell in the nextcolumn but same row or the unit cell in the next column and the rowabove; each unit cell in adjacent rows is an exact duplicate of the cellbut inverted; each unit cell in the other rows routes an input signaleither to the unit cell in the next column and the row above or the unitcell in the next column and the row below.
 3. The device according toclaim 1, wherein the MEMS actuator moves the end of the furtherwaveguide relative to either the second distal end of the curvedwaveguide when the further MEMS actuator is in the first position or theend of the another waveguide when the further MEMS actuator is in thesecond position; the another MEMS actuator moves the end of theadditional waveguide relative to either the end of the curved waveguidewhen the further MEMS actuator is in the first position or the end ofthe waveguide when the further MEMS actuator is in the second position.4. The device according to claim 1, wherein the MEMS actuator andanother MEMS actuator are rotational MEMS actuators.
 5. A devicecomprising an optical switch comprising: a MEMS actuated suspendedwaveguide platform incorporating a waveguide and another waveguide whichform a crossover wherein an end of the waveguide is disposed at a firstpredetermined location on the MEMS actuated suspended waveguideplatform, an end of the another waveguide is disposed at another firstpredetermined location on the MEMS actuated suspended waveguideplatform; a curved waveguide where one end of the curved waveguide isdisposed at a second predetermined location on the MEMS actuatedsuspended waveguide platform proximate the first predetermined locationof the end of the waveguide and a second distal end of the curvedwaveguide is disposed at another second predetermined location on theMEMS actuated suspended waveguide platform proximate the another firstpredetermined location of the end of the another waveguide; a furtherwaveguide disposed upon a first predetermined portion of a MEMS actuatorwhere the further waveguide has an end disposed at a predeterminedlocation on the MEMS actuator; an additional waveguide disposed upon afirst predetermined portion of another MEMS actuator where theadditional waveguide has an end disposed at a predetermined location onthe another MEMS actuator; and a further MEMS actuator to linearlytranslate the MEMS actuated suspended waveguide platform such that theMEMS actuated suspended waveguide platform moves relative to the MEMSactuator and another MEMS actuator; wherein a separation of the firstpredetermined location of the end of the waveguide and the secondpredetermined location of the end of the curved waveguide is the same asanother separation of the first predetermined location of the end of theanother waveguide and the second predetermined location of the distalend of the curved waveguide; in a first position the further MEMSactuator positions the MEMS actuated suspended waveguide platform suchthat the further waveguide is coupled to the second distal end of thecurved waveguide and the additional waveguide is coupled to the end ofthe curved waveguide; and in a second position the further MEMS actuatorpositions the MEMS actuator suspended waveguide such that the furtherwaveguide is coupled to the end of the another waveguide and theadditional waveguide is coupled to the end of the waveguide.
 6. Thedevice according to claim 5, wherein the MEMS actuator moves the end ofthe further waveguide relative to either the second distal end of thecurved waveguide when the further MEMS actuator is in the first positionor the end of the another waveguide when the further MEMS actuator is inthe second position; the another MEMS actuator moves the end of theadditional waveguide relative to either the end of the curved waveguidewhen the further MEMS actuator is in the first position or the end ofthe waveguide when the further MEMS actuator is in the second position.7. The device according to claim 6, wherein the MEMS actuator andanother MEMS actuator are rotational MEMS actuators.